Dr. Goodman's Foundation Work
The infamous 12 minute FT video with over 2.5 million views on YouTube and still going. Originally created in 2011 for Lance Armstrong before those other things happened. Access it here with all of our other content saving you from navigating to another app or website.
This doesn't take a lot of time but it's challenging and works. The focus is all on the posterior chain (read back, glutes, hamstrings).
This will make you a stronger swimmer, a better handler on the bike, better climber, and help cut out lower back pain. These are the muscle groups that endurance athletes often ignore, and pay the penalty for late in a race.
Do some foam rolling and stretching after the foundation routine/before strength work.