This would depend on the outcome of the statutory residence tests.
You will need to review the guidance and take the tests and confirm if split year treatment applies.
If you are not resident for the full tax year only declare your UK income from the date your arrived in the UK.
If you are considered resident, you will then need to consider whether split year treatment applies, if it does, you claim this via a Self Assessment tax return and only declare your UK income from the date you arrived.
If split year treatment does not apply , you will need to declare your German income and claim a tax credit for any German tax paid.
RDR3 Statutory Residence Test