How to remove a device from a sync chain
Go to Settings->Sync (or navigate to
brave://settings/braveSync/setup). If you don't see a list of devices in the sync chain the device is not in one, and there is no reason to do anything else listed here.
Find the specific device in the list you want to remove and click the cross in the Remove column.
Find the specific device in the list you want to remove and tap the garbage can icon.
You will be asked if you want to remove the selected device from the sync chain. Click/tap OK.