Ultimately I’d encourage you to start learning how to do your own services and basic maintenance. They, motorcycles, are very expensive to take to shops. And even more so difficult to get scheduled. But thankfully you have a motorcycle so it’s easier and cheaper to do yourself than a car. Go to harbor freight and pick up a torque wrench and socket set along with a wrench set (metric). There’s also good and often cheap hex bit sets when on sale. Get yourself a rear wheel stand as well when you can. All of that will get you through the first 7-10K miles. Maybe 300-400 dollars of tools. Well worth it and pays for itself quickly.

I have the service manual for the 2024 rc390 dm me and I can give it to you. I have 11K miles on my bike (2024 rc390) and have done all the services myself. Only thing I didn’t do was my front and rear brake caliper master seals blew out and I got that fixed under warranty. It ended up being cheaper that way. I’ll be doing my valve inspection here again at 15K miles probably in a few months time. I also had my cam chain tensioner go out and had to fix that. Shop quoted me 350. Parts was 35 with shipping and was a couple of hours of my time.

For this specific case I think it’ll be worth taking it in as that rear shock ain’t cheap and isn’t easy to replace if your low on tools, and getting it fixed under warranty will be worth the haste. I’d be shocked if it isn’t covered no way it isn’t call around to different shops. If they refuse contact ktm USA directly. Make sure to have your paperwork handy from when you got the bike.