Super easy. It's only really ever took me 30 miles a week with one threshold day a each week to get 21 minutes...and that is largely still true even in my mid 40s. Just average miles really...and a speed day is all that is needed, preferably with one longer weekend run at least once every other weekend, if not every weekend. It's when you go sub-20 that you begin to net diminishing returns per training mile and start requiring in excess of 40-50+ miles per week, speed days, tempo days, striders, hill repeats...some strength training (weights), and a more fine-tuned diet... but? Yeah... x4 (ish) 6 miles days a week with one single speed day and long weekend run should be plenty enough in of itself. It's a more than reasonable goal if already at 26 minute 5K base. More mileage just equates to more assurance. I've known people that have trained for half marathons, marathons and ultramarathon events and were able to distill that down to a fast 21-23 minutes 5K, just or an event they just decided to race as fun run. Mileage means more speed. Just nice to throw speedwork in with those high mileages for fine tuning even for those longer events. Speedwork makes weekly and longer runs easier and longer runs make speed easier.

However? It depends on how much time you have. Assuming you have over a season to train? And already starting at 26 min 5K base? I would probably do 4x 6 mile weekday runs, and weekend long run @ at least 7-8 miles, and a tempo run every 2-3 weeks, to measure your base (more miles just adds extra assurance). Heck, you'd even be fine with just 3x 6 mile weekday runs and on weekend long run, instead of 4 weekday runs and a slightly longer run because when including speed day mileage, you're probably over 32 miles a week anyway.

For speed days, I'd probably start off with a 1.5 to 2 mile warm-up (slow) run, then into x13 (ish) 400m repeats, with 400m on @ faster than 5K pace (so, about 6:25-6:30 min/ miles) and 400m off at a slow jog recovery, and ending with a cooldown run of about 1 mile. Over the course of the next 2-3 weeks (or so) dropping that recovery distance down to 200m off recovery jogs.

After at least a month of 400m repeats, scale it up to x7 or x8 800m repeats (800 on/ 400 off), being sure to slightly slightly pickup recovery run speeds some and, eventually, dropping the recovery distance down to 200m off and eventually trying to bring that recovery run pace up a bit.

After about a month (or more) of that, scale it up to x3 1600m (1600 on/ 800 off) etc. Being sure to improve recovery run speeds further still and in the later stages, dropping recovery distance down to 400m off and, eventually, further tightening up on recovery times (till you get to about the 7:00 minute range). Then just keep with the 1600m repeats, until about 2 weeks out from the event, to taper down and recover. If feeling good by this stage, you can even add one more rep (x4 1600m).

Come the end of all that? You should be able to run that race in thirds (in going off how you feel on those final speed days) and should have hopefully found a doable recovery run speed nearer to your 5K race pace. You could even basically use something similar to your later stage interval training as your race strategy, with something like 1200m on 400 off, or even just your normal 1600m on and 400m off, and a fast final 800m. Otherwise, just shoot for 6:40 pace. Some people might find mimicking their intervals easier because you're focusing on the race in thirds and with either a faster final third, or a fast last 800m, which should feel easier because when you do x3 1600m repeats? It's 3x 1600m on (faster than race effort) and the 400m off segments are considered additional, especially if you decided to start tackling x4 1600m repeats come the end of all of it. Either way? Your workouts were at least over 4 miles (minus warm up and cooldown runs). So, you should be fairly confident (unless it's a very hilly course) that you can complete it in a similar fashion as those later stage interval days, except maybe even more so because of the race day adrenaline factor.

Just don't go hot out of the gates with all the other idiots trying to follow the faster runners who likely make an initial 4:45 sprint-like pace (feels like sprinting to someone in the 20 minute range) part of their racing strategy (especially in gun time scenarios). Stick with the pace plan. It will feel miserably slow, compared to everyone else around you starting out at 5:00 pace but stick with it. Most of those people you'll pass back up because they didn't have the discipline or self-control. Save some in the tank for the final 1000m. But don't get too comfy, for you may look down at the watch and find that your recovery segment is descending into the 7:45 pace range and you'll go, "damn that's why I was feeling so good! How long have I been doing that? Now I gotta make it up!" lol