To submit the supplementary form SA109 for tax year 2020-2021

Hi, I have filed my tax return online and paid the tax for the year 2020-2021. I was qualified for the split year treatment for that year but I did not know that I need to submit the form SA109 in paper format at that time. I found that I may need to submit the form for my split year treatment. Could I just submit the form through post now? It would be very kind if anyone can give me some advice. Thank you.

Hi zymc,
Yes, you should now submit the 2021 SA109  with a brief explanatory covering letter.
The paper version of the 2021 SA109 can be accessed here:
Residence, remittance basis etc (Self Assessment SA109)
Thank you.