How to un-reconcile a vat quarter which has altered to a two month period

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I have reconciled the lastest VAT quarter which I thought was May-July, after I had completed and reconciled that quarter and began the submission process, I was told the dates did not match.  I needed to only do a two month return, May and June which I had requested some time ago but had not received any notification this change had been made.  My question is how do I un-reconcile a VAT quarter (May-July) in order to submit the correct period (May - June)?