If you mean you have actually generated parts using File / Parts but now want to remove the part while keeping the staff in the score, go back to File / Parts and you can remove it. Or if you want to remove the instrument completely form the score, go to Edit / Instruments.
If none of this helps, please attach the score you are having trouble with and explain what you are trying to do in more detail.
Comments
need more info
See https://musescore.org/en/handbook/part-extraction, if that is what you mean.
Or https://musescore.org/en/handbook/create-new-score#instruments-and-voic…
If you mean you have actually generated parts using File / Parts but now want to remove the part while keeping the staff in the score, go back to File / Parts and you can remove it. Or if you want to remove the instrument completely form the score, go to Edit / Instruments.
If none of this helps, please attach the score you are having trouble with and explain what you are trying to do in more detail.