This only needs to be done if your financial year does not start on 6 April. Select MTD > Self-employment* quarterly update > Options > Reporting period option > Calendar 1 April to 31 March > OK:

*Or UK Property / Foreign property if you are submitting a quarterly update for those income sources
Note:
•This only needs to be done once (as the setting is saved in the VT Transaction+ data file), unless you decide to change back to standard quarters.
•Any change must be done before submitting the first quarterly update of a tax year, otherwise you have to wait until the next tax year.
•The change is communicated to HMRC through the software, which updates the dates on HMRC's record of your income tax obligations. To view the record, click on Income tax obligations? or select Taxpayer > Income tax obligations. The change should be reflected immediately. If it is not, click on the Refresh button. If it has still has still not updated, this indicates a delay at HMRC's end, in which case check the MTD errors page for details of any HMRC service issues.

•Changing the reporting period from standard to calendar (or vice-versa) must be done in the software and cannot be done through HMRC online services.