How would one get back into swimming? I swam competitively for

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How would one get back into swimming? I swam competitively for my highschool team.

23 now, 6'2" 180lbs. Haven't worked out since I was 20 but I'm still toned besides a bit of flab on my stomach. Mostly because in my free time I eat magic mushrooms and climb trees all day.

I smoke half a pack of cigarettes a day, but I smoked a pack a day in highschool. That didn't really affect my swimming since my times senior year were 53.8 for 100yd butterfly, 58.4 for 100yd breast stroke, 47.6 for 100yd front crawl, and 1:46.2 for 200yd IM.

Would the best thing to do just find my old work outs form highschool and go at it again? Or should I focus on lifting/cardio on dryland before hopping in the pool?

I mostly want to break under 50 seconds for 100yd butterfly since that was my goal, but I tore my shoulder and had to go to physical therapy.