The VAT quarter can only be opened back up if the submitted date is empty, this will need to be done in the background by Accounts Support.
Please raise a new case online and reference the title of this article and then we can amend this for you.
If you are just needing to get the figures to be able to submit the VAT, this can still be done if by mistake you have closed the quarter.
You just need to REBUILD the data on the DETAIL tab, then go onto the MTDSUBMIT tab and go through the usual steps.