You could just make a payment from the private bank account into the business account and then process that receipt as if it was from the client to the appropriate invoice. The Private account would then have a matching (cancelling out) deposit and payment,
Or, if you wont to keep the funds in the private account then you would do a Journal.
Debit - Equity account for a sole trader/partnership or Shareholders Loan account for a company
Credit - either Accounts Receivable + Invoice or Customer Credits + Supplier as per normal
As your situation doesn’t involve expenses/suppliers/payment of personal funds or reimbursements - expenses claims aren’t required
PS: have assumed your reference to “creditors tab” was meant to be Customers tab as all your other commentary relates to Clients