Determining weights for supplemental lifts

For the beginner programs in the App, the program will call for lifts I.e. Good mornings at a specific percentage i.e. 75%. Is there a way to determine such numbers without spending a ton of time determining a 1 RM for every lift in the app?

Thanks!

Pick some weight during a workout and record what you do. The app will use that to estimate 1RM and 75% of that next time.