Self assessment or Add a missing employer

I am technically a UK resident and am studying at university (I have 1 year remaining). This year I am fortunate to be able to do a placement year in Germany. I am paid a salary to sustain me (a total less than £12,558). I started in September and spent a lot of time getting setup with visas, health insurance etc, but now must sort my tax. I believe I need to fill a self assessment form but have also noticed an option to 'Add a missing employer', within the 'check your income tax' tool. Should I do both or only 1? Also, at the following link https://www.gov.uk/tax-foreign-income/taxed-twice does 'Apply for tax relief before you get taxed on foreign income' mean before taxed by the UK or before being taxed by Germany, because I have already had a paycheck which was taxed by the German system. Thanks ever so much

Hi

If you are living in Germany at the time you are working for the German employer, you would only be taxable on the German employment in Germany.  
You will need to consider your residency status in the UK.  
Please review the guidance at RDR3 and undertake the statutory residence tests:
RDR3 Statutory Residence Test.  
Depending on the results, you may still need to dislcose the German employment on your tax return.

Thank you