There isn’t a way of doing this directly, but you could use a holding account to effectively transfer the balance.
In this sense, you would set up a holding bank account within QuickFile, refund the balance from one client, and re-apply it from another.
For example, if I have Client A with a balance of £50, and Client B with no balance, I would firstly create a Holding Bank Account within QuickFile (if I don’t have one already).
Then, I would locate Client A, go to View >> All Payments, and do an Advanced Search for those that are unallocated. When I view these, I can refund them to the holding account.
From the holding account itself, you will not have a “money out” transaction matching the refund to Client A. Now I would create a new transaction of the same value coming back in, and tag this as a prepayment for Client B.
I hope that makes sense?