Deletion

See: https://musescore.org/en/handbook/3/voices#delete-hide-rests
https://musescore.org/en/handbook/3/tools#timewise-delete

Generally, you don't delete silence, you replace it with sound. So deleting a rest would not normally ever come up - just enter notes, and the rests go away automatically. It's kind of like asking, how to delete white paper in Micrsoft Word - you don't, you just type and the white paper gets covered automatically.

That said, you maybe you are in some special situation where there is a rest that shouldn't be there. In order to understand and assist better, we'd need you to attach your score and explain your situation in more detail.