If you’re filling out your self-assessment as a non-resident, and wondering where your personal allowance has gone, read on…
You won’t automatically get a personal allowance if you’re not resident in the UK.
This HMRC page will give you more detail along with a claim form that you can possibly use if you hold a British passport or you’re an EEA citizen: https://www.gov.uk/tax-uk-income-live-abroad/personal-allowance
There are also provisions under Double-Taxation Agreements with some other countries that will automatically add back your personal allowance. Boxes 15 and 16 on the SA109 form ask about this.