How do i flip the screen on a chromebook without losing anything?

if it's a flip-over one in tablet mode, it'll rotate itself as you move it. there's an auto-rotate toggle in quick settings (bottom right, the clock) to lock it.

ctrl + shift + refresh (the circle arrow key on the top row). each press turns it 90 degrees, so keep tapping until it's back the right way. nothing gets lost, it only changes the display. if the shortcut feels too easy to hit by accident, Settings > Device > Displays has an orientation dropdown that does the same thing.