Hi Vnfwg33d,
If the ISA is a flexible ISA, you can return the money back into the ISA and not impact your £20000 allowance.
If you take the money out of the ISA and place in another ISA, this will be part of the £20000 that you can save each year.
Please have a look at the guidance here:
Individual Savings Accounts (ISAs)
Thank you.