Normally self-assessment tax returns need to submitted by 31 January, otherwise there is an automatic £100 late filing penalty.
However, HMRC announced that provided 2020/21 tax returns are received by the end of February, the late filing penalty will not be applied. Filing late will, however, extend the period during which HMRC may open an enquiry into your return.
You also have longer to pay your personal tax
2020/21 income tax, CGT, class 2 and 4 NIC liabilities normally need to be paid by 31 January 2022. However, HMRC have also announced that provided the tax is paid by 1 April 2022, there will be no penalty, although interest accrues from 1 February 2022 at 2.75%.
If you need longer to pay, then you will need to agree a payment plan with HMRC.