Multi-rest bars

Just add more measures, or delete them (the latter requires you to turn off multimeasure rests temporarily, by pressing M), the number gets updated automagically (Computers in general and MuseScore in speacial is better at counting than humans ;-))

See https://musescore.org/en/handbook/3/measure-operations#break-multimeasu… and https://musescore.org/en/handbook/3/measure-rests#break in the handbook if you want to break a muli-measure rest.

If you accidentallly added 7 empty measures when you meant to only add 4, simply turn off multimeasure rests by pressing "M" then delete the three extra measures by selecting them and pressing Ctrl+Delete. Of course, that affects all parts in your score, not just this one. So if the problem is actually that you entered the notes for this part three measures too late, easiest would be select them and cut and paste them to the proper location (easdiesty to do that in the score, not in the part).

If on the other hand you simply want to break up the rest to show 4 then 3, this happens automatically if you do any of the things that normally should cause this - a double bar, rehearsal mark, tempo change, etc. So simply add the missing marking (again, easiest to do that in the score) and the rest tasks care of itself.

If you still have trouble, please attach your score so we can understand and assist better.