Just enable coin control, select the unconfirmed input, spend it by sending to yourself, and add a significant fee.
You can do the same thing by right-clicking on the unconfirmed transaction and selecting "Child pays for parent". There is no need to use coin control.
Doing CPFP in this way is easier for someone without technical knowledge and the other advantage is that the user would see the effective fee rate before broadcasting the child transaction and wouldn't have to calculate that manually.
Thanks, I did it like this and it was indeed very easy, and it succeeded. The transaction is now confirmed.