your personal +Drive contents are probably lost forever.
that’s a shame.
but the factory sound banks & project can be restored with a factory reset:
switch A4 OFF
hold FUNCTION
switch A4 ON
wait for the menu to appear, then press trig button 3.
imo, the +Drive format option should be less easy to trigger accidentally.
all you need to do is GLOBAL > scroll down >> hit YES twice… this is much too easy!