How can I submit a VAT return in MTD with another date. The dates on the next return cannot be changed. But HMRC are asking me for a specific date of a missed return?

Let me provide some information about VAT return, @communityoil.

It is right that changing the dates on the next return is unavailable. 

Let's say you need to have your VAT returns in March, June, and September, you will need to set up your VAT so that the Start of the current VAT period is showing as October. This will set up the quarters so that you can file in December, March, June, and September going forwards.

Then, in filing a late return, you'll need to submit it outside QBO. For your reference, please check out this article: File your VAT return and record tax payment in QuickBooks Online.

Let me also attach this link to guide you submit a return and how to mark it as filed in QuickBooks: QuickBooks VAT return guide.

Feel at ease to get back to me if you need more VAT insights. I've got your back always.