transposition from Bass to Treble.

Copy and paste may be enough?
https://musescore.org/en/handbook/copy-and-paste
then highlight the measures and use up arrow (https://musescore.org/en/handbook/transposition#chromatic-transposition… ).
Welcome

It's not clear what you mean. If you have two staves currently - one treble and one bass - and you wish to copy the contents of the bass clef staff to the treble clef staff, then indeed, copy and paste works, and then you'd probably want to raise the pitch an octave with Ctrl+Up. If you mean, you have *one* staff that is current bass but you want to change it to treble, simply add the treble clef from the Clefs palette - and again, you wi,l then probably want to raise the pitch of everything on that staff an octave.

To clarify:   Internally, within the MuseScore system, notes have an absolute value:   for example, the note is not merely C, but C3.   That note will then be expressed appropriately upon whatever type of staff it sits on, such that if you change the staff-type the notation will change appropriately (while the playback sound will not change, since the note itself has not changed).

Hence, you can copy-and-paste notes to different staffs, but that operation alone will not change their value.   Thus, the next step is probably to shift the pasted notes up-or-down by octaves, changing the value of those pasted notes with the notation following suit.   On playback, the adjusted notes are clearly sounding in a different octave.