Late submission of Self Assessment

I'm a new migrant to the UK. I have only realised that I need to file a self assessment recently. I sent a paper form SA109 for applying split year treatment last week. Knowing that the deadline of self assessment is 31 January, could you kindly advise whether I can submit a separate SA109 and self assessment via online platform and withdraw the paper form now? Thank you for your help.

Hi,

The whole return needs to be submitted together, either fully online or fully by papar. You can use 3rd party software to submit online to include the SA109.

https://www.gov.uk/government/publications/self-assessment-commercial-software-suppliers

Thank you.