Our merge function works by deleting one transaction and then adding the transfers to the other transaction, to combine everything in one.
You can't directly unmerge the transactions once they have been merged, but you can restore the deleted transaction, and then remove the excess transfers from the second transaction.
You can find deleted transactions by using our search function and clicking the box under "show deleted transactions."
Restore the deleted transaction by clicking the "..." icon, and then remove the excess transfers from the other transaction.