erace something

Why would you want to delete a rest?
It is possible, using Ctrl+Del, but may not be what you really want.

One doesn't "erase rests". You put notes on them to replace them.

Probably you want to shorten the measure. Then you've several options:

• insert the corresponding time signature: https://musescore.org/en/handbook/3/time-signatures
• change the actual measure duration: https://musescore.org/en/handbook/3/measure-operations#duration
• switch to the "insert note input mode" and press "del": https://musescore.org/en/handbook/3/note-input-modes#timewise

Rests only can be deleted in voice 2, 3 or 4, not in voice 1, see: https://musescore.org/en/handbook/3/voices#delete-hide-rests

Or you want to move forward some notes, then select these notes (https://musescore.org/en/handbook/3/selection-modes), copy (ctrl+c)/cut (ctrl+x) and paste (ctrl+v) it.

If you're familiar with MuseScore, you'll realize, that's very simple. For further questions please attache your score and describe, what you want to do.

(note: the amount of references doesn't mean, that's MuseSore is very complicated, rather than music notation is an own language and needs time to learn ;-)

As mentioned, erasing a rest doens't really make sense, f you literally did that you would have too few beats in the measure. My guess is you really want to take some number of subsequent notes and move them earlier. That is done using cut & paste.

If you attach your score and describe what you want to do in more detail, we can understand and assist better.

Meanwhile, I highly recommend reading the Handbook, watching the various tutorial videos, etc, to learn the basics of using MuseScore.