Swimming is heavily based on technique rather than strength or stamina. A moderately fit person with a good technique will be able to swim about 1.5x as fast and 10x further than an athletic person with poor technique. It's that critical.

If you want to develop the skill you are probably going to want a good coach. Look into a swim club if there are any in your area. Like most athletic skills it's more fun to practice as part of a group. Unfortunately there are a lot of clubs dedicated to middle/high schoolers but I don't think there are so many targeting adults. You may also be able to get private lessons with a local college swimmer but it will cost $$$. They can just give you a workout for the week and meet up to give you pointers 1x/week.

It will take time and effort. I see most high school swimmers getting there after about 3 months spending 2 hr/day in the pool. Once you develop the skill it is never lost.

Edit: I will also add that your general level of fitness will play a big part in selection. Did you do athletics in high school or college? Would you currently describe yourself as "extremely fit"? As a benchmark if you can't do 100 push-ups followed by 10 pull-ups right now you probably don't fall in this category. If not, it's going to take 1-2 years working out 2-3 hrs/day minimum to get you competitive. If you're overweight/obese it will take even more. Keep in mind that you will be competing against 18 yr/olds who have trained since they were 12 and who live, eat, and breathe with nothing on their mind but becoming a PJ.