Any split, of any kind, can be undone as long as the tabs have not been paid.

Steps

1. Open the ticket.
2. Tap Action, then tap Split.
3. In the Split Ticket screen, tap Remove Splits.

The POS removes every split from the ticket, merges the items back onto one tab and returns you to the Ticket screen.

If this does not work

If Remove Splits is unavailable, one of the tabs has already taken a payment. Void or refund that payment first, then remove the split. See Refund a paid ticket.

Source: Global Payments Genius POS User Guide. Newly built article, pending review.