Thanks so much for these helpful instructions! I'm a different (newbie) user with the same problem. This solution looks good to me, but is there a different way to do it for Quickbooks Online?

Like skibumps, I just added several transactions as deposits, with a customer in each payee field. I then went through the bank register to make sure that each deposit was linked with a customer (in the payee field). All of that seems to have saved just fine, but when I go to the "Customer" section, the transactions have not been matched to each customer.

From now on I certainly won't go this route! But is there a way to fix what I've done without re-doing everything?