If you need to undo the syncs, you can easily and quickly rollback any transaction. Rollback will completely take the transaction away from your QuickBooks/Xero account, not causing any damage to your QuickBooks/Xero data.
1a. To rollback several transactions, in the Transactions tab select the transactions needed as pictured.
You can also show up to 100 transactions per page, if needed
1b. Alternatively, if you want to rollback all click square selector on the Txn Info (1) and Roll Back transactions on the page, or use the option to Roll Back all transactions on all pages (2), which will be available after all transactions per page are selected.
2. After you selected the transactions needed just click Batch Actions menu and click Rollback.