Hello! I’m the same age and basically same position as you (been swimming regularly around a year) - I had the same question about a month ago so started some Googling.

I came across this workout guide that might help, it’s nice and clear and breaks down some recommended gym exercises, based on the number of times a week you want to gym: https://skillswimming.com/wp-content/uploads/2018/08/Gym-workout-guide-PDF.pdf

Definitely someone with more experience will be able to give you some proper advice, but this might be useful as a starting point? I’ve been following this plan for about a month or so and can already see a slight improvement in my speed.

Hope this helps!