You choose which to keep. If they changed a different box, both changes are simply kept – nobody's asked. If you both changed the same box, you'll see both side by side, marked yours and theirs, with Keep mine, Keep and their name (such as Keep George's), or Let me look first. For example, say Grandad George changed his own birthday while your change was waiting – pick whichever is right. If you keep theirs, yours isn't lost: it goes to "Changes you let go" on that phone.
Where to find it
Under Children → What are you trying to fix? → Something else… → Dave is the wrong person… → the rows for each family member
Only people with the "Add people" and "Remove" ticks.
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