Is there an 'easy way' to reverse out a grossup payment?

Some employees were mistakenly paid some grossup payments last month and they need to be claimed back / reversed out.

We don't have them set up for retro as had issues with it historically.

Entering negatives into this month gives me an error on the 'process separate' quickpay.

I suspect we will have to manually unpick it, but thought I'd ask the question here before we start doing that.

Thank you!

Mandy