It depends on if you are trying to transpose all of the notes, or only insert a key change. To transpose the notes see https://musescore.org/en/handbook/3/transposition. If you only want a key change, then drag the key signature to the measure where the new key signature starts.
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It depends on if you are trying to transpose all of the notes, or only insert a key change. To transpose the notes see https://musescore.org/en/handbook/3/transposition. If you only want a key change, then drag the key signature to the measure where the new key signature starts.