I'm not sure there is an invert button, although "ctrl-r" rotates a stamp, maybe that was it? I hope there isn't an invert button already, I spent quite a while learning Lua so I could make an invert script...
at school sometimes i accidentally turn the screen upside down
and got in trouble
but i still found out its
alt+up key
if that doesnt work than try these combos:
alt+down key
ctrl+alt+up key
ctrl+alt+down key
I think it's the tpt SAVE, that got inverted.
Maybe copy a piece (ctrl+c), and rotate it, (ctrl+v, ctrl+(shift)+r)