What do you mean with "easy" for the rest timer?
The timer will suggest different rest periods based on whether the previous set was "easy" or "hard".
Easy means you think you could have done 1-2 extra reps on the last set. Example: you finished Squatting 5 reps but it felt like you could easy have done a 6th or 7th rep. In this case the set was easy, so you don't need to rest that long before doing your next set. You can just rest the default 1:30mins.
Hard means you had to work hard to get your 5 reps on your last set. Example: you finished Squatting 5 reps but it didn't feel like you could have done a 6th rep with that weight. In this case it's better to rest longer, 3mins before doing your next set for that exercise.
If the last set was very hard, it makes sense to wait longer than 5mins before doing your next set for that exercise. Example: you barely were able to get 5 reps on the last set. The app will tell you to rest 3mins in this case because you did get all 5 reps. But it's best to wait the full 5 mins in this case so you're less likely to fail on the next set of that exercise.
Note that it takes a while to develop a "feel" for how easy/hard a set is. If you're just getting started and can't feel the difference yet between a hard and easy set, just rest the default 1:30mins between sets.