Every change shows in Recent Activity, with who made it. The owner can put back everything one person changed since a chosen day, or take away their edit rights until things calm down.
Where to find it
Settings (bottom row of the top bar, far right) → Recent Activity
Only people with the "Undo saves and restore" tick.
On a phone: if the Settings tabs are tucked away, press ☰ Menu (top left) first.
Still stuck? Talk to a real person: send us a message, or email support@mywholefamilytree.com