How to move all the notes across

Hard to tell from an image. Right after this happened, you could have hit the Undo button in the upper right. Otherwise you might be able to C+P the notes back where they belong. Or, maybe delete the measure in front.

Fix what? There is no place in the image where notes are obviously in "the bar behind them".

Please attach the score itself (.MSCZ file), identify exactly where the problem starts and ends (e.g., measures 253-331, in the oboe and bassoon staves), and describe what it should look like (e.g., the notes should begin on beat 2 but they begin on the previous measure's beat 4 instead).

That said, @bobjp's suggestion to copy/paste the notes back to the correct position is likely to be how it gets fixed.

Try reading the Handbook section about Copy and paste:
https://musescore.org/en/handbook/4/copy-and-paste