BTW, solo instruments normally get moved to the "proper" (for the selected genre) location automatically if you simply press the "make soloist" button. So for orchestra, that means, right above the strings, but in other genres, it might mean the top of the score.
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Press I and in that dialog move the staves to your heart's content.
See https://musescore.org/en/handbook/3/create-new-score#change-order-innst…
BTW, solo instruments normally get moved to the "proper" (for the selected genre) location automatically if you simply press the "make soloist" button. So for orchestra, that means, right above the strings, but in other genres, it might mean the top of the score.