Undo a wrong bank assignment

Firm owners, firm admins, accountants and bookkeepers may do this; other roles are refused. Nothing needs switching on.
A line that is only partly assigned shows "x of y assigned, z open" and its assignments right in the list under Bank lines. A fully assigned line leaves the open views: choose All lines, find it (search by amount, name or reference), and click Open line. The page of the line lists its assignments.
Click Reverse on the wrong assignment and confirm with Yes, reverse. The question names the amount and says that a reversal row is added.
Nothing is deleted. The original row stays, struck through and marked reversed, next to a new row labelled Reversal with the negative amount, dated today. The payment the assignment booked on the invoice or receipt is taken back, so the line has its open amount again.
It is refused when the current month is closed, and a row that is already reversed, or a reversal row itself, cannot be reversed. Then the page says that the assignment could not be reversed or names the closed month.
If a bank rule made or learned the assignment, the rule takes the undo into account.
Afterwards assign the line correctly with Match or Assign manually.