I change the "First Month of the tax year" to April 1 but it keeps reverting to April 6. My year end is 31st March. I will be using Quickbooks for MTD ITSA in the UK

Using other supported browsers is a great way to isolate cache-related issues, Zecnavda. Since that didn't work and the first month of the tax year is still reverting to April 6, I recommend reaching out to our live support team through the Help icon. They have tools to securely check your account and see why you can't change the date.

The comment section below is open if you need further assistance managing your accounting periods.

I have queried this with quickbooks and this is their reply

"Thank you for being a valued QuickBooks customer and for your patience while our teams worked on the behavior you have encountered changing the to the 1st April for your tax year.

The engineering team have now completed their investigation and have advised at this time that the resolution to the behaviour you are experiencing will need to be treated as and included in an enhancement project.

We do not have a time frame available for enhancement projects but please rest assured that this will be prioritised against ongoing work.

In the meantime, please do not hesitate to reach out to our support team for any additional queries.
 

There will not be any additional updates provided regarding this investigation"

All in all not very helpful and no idea of timescale. I'm sure this will affect a lot of users as many will have 31st March year end