Sales credit notes & VAT

Hi,

I have a client who uses a ClearBooks. They are on cash accounting for VAT and posted sales credit notes. I can see the VAT on these credit notes is sitting in the VAT cash control account however they have not been pulled through on subsequent VAT returns. Is there a reason for this and how does my client correct this so the VAT clears from the VAT cash control account to the VAT control account and ultimately the VAT return?