Where exactly are you seeing the Mac pinned in China — in Find My, Maps, or a website? That matters here.
If it’s Find My or Maps, try connecting the Mac to a different Wi-Fi network or your phone’s hotspot. Then check System Settings > Privacy & Security > Location Services and make sure Location Services is on. Macs use information from nearby Wi-Fi networks to determine their location, so incorrect Wi-Fi location data can sometimes put the Mac in the wrong place.
Also check the location timestamp shown for the Mac in Find My.
I wouldn’t erase it again or sign out of your Apple Account at this point. If it still shows China after trying another network, let us know exactly where you’re seeing that location and whether the timestamp is current.