Hi Joshua O'Sullivan,
You will need to review the guidance on residence (RDR3 Statutory Residence Test
) and take the residence tests to determine your residence status and whether split year treatment applies. If split year treatment applies, you would complete SA109 (to claim split year treatment) along with the rest of your tax return and you would not include your earnings in Ireland.
If you are resident in the UK for the full tax year and split year treatment does not apply, you would declare your Irish income on SA102 and SA106, so that you can claim a foreign tax credit.