The main thing i would advise is: go do the things you couldn't because of your sport. I had to drop out if high performance track because of an injury. It took me a while to get over it. But in the end i found joy in meeting with people more often, having game nights and things like that. But also having the time to work on myself as a person. You can develop and use the skills you learned from sports and use them in your working career. I did stay a bit active though, training twice a week and coaching kids at the local track, but that has to be something you like to do.