Hi,
The SA109 is used to claim non residence, split year treatment and remittance basis, as well as claim personal allowances where you meet the criteria.
You have to decide whether split year treatment applies to you, before you submit your tax return. HMRC will not make that decision for you. If you have reviewed the guidance and split year treatment applies, you claim it in your SA109 along with the rest of the tax return. You can find the guidance and statutory residence tests here:
RDR3 Statutory Residence Test
You cannot use the HMRC online tax return if you have to submit the residence section. You either submit the whole tax return on paper or the whole tax return online, by buying commercial software. You can only use the commercial tax return if you have a government gateway user ID and password or can obtain one.
If you cannot verify your identity, you have no choice but to submit a paper tax return. You can find a list of commercial tax return suppliers, as well as paper returns to download, here:
File your Self Assessment tax return online
Thank you.