I don't think you can... I have multiple instances of this issue dating back months.
You can obviously change/edit the leave within the pay run, but it'll be stuck showing as "Partially Paid" of the leave request screen.
It is a very common scenario in case of Annual Leaves. Employees can decide not to take leaves for the pre approved leaves.
The solution I provided to the client before is to create the 'Adjusted Pay' for the pay run in which partial leave was paid. When your adjusted pay gets open you undo the imported leave. This will free up the leaves and then you can edit it. Then you can reimport in the adjusted pay. This will not impact the leave payment but a workaround to change the leave status.
This time client is not happy with the process since it is lengthy and includes touching the already paid(correct) pay run.
Oh, I was not aware that an Adjustment Pay would fix the issue.
You could try clicking the "Set Pay Period Date" or the "Map To Pay Run" buttons on the Leave Administration screen, but that does not always work.
