how to change to bass clef

Simply witéh PALET-CLES (in French).

Select first measure the stave you want, and double click the CLE icon.

If you have Pb too high or to low, change all the stave (select the first measure and Sélect + shift the last) and use CTRL+ up arrow or down arrow for one octave up or domwn

see also: https://musescore.org/en/handbook/clefs#add

Changing the clef is easy enough, just add it from the palette. However, you have an additional problem you will need to correct - you actually entered the wrong notes. For instance, the first note in the first measure was almost certainly intended to be a "C" but you entered an "A", presumably because you didn't notice the clef was not what you intended and didn't hear it in the playback. So you will need to also change all the notes. Lukcily this won't be hard for a simple example like this. Select the contents of the staff and use Alt+Shift+Down to move the pitches down one line/space at a time until they are where you want them to be.