Outdoor Run Function Lost in Activity App

The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

The next steps would be to unpair and pair your watch again and restore from the backup:

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

If you mean they're missing from your workout list then scroll to the bottom of that list then tap on add workout and select your workouts from the list of 78 workout types,this will put the workout type back into your list.