Adult Swim lesson Recs?

I know how to swim, but would just consider myself average. Looking to become a really strong swimmer so was looking for adult swim lessons y’all recommend. I want to get my diving certificate so want to be confident in open waters in treading. I know the training usually consist of swimming certain distance & treading for 10min. Also have aspirations for triathlons, but the swimming part always discouraged me. TFA!