Temporary second job with BR code but I'm a higher rate taxpayer

I work as an academic at a UK university. Last year I was invited to be external examiner for a PhD thesis at another university and I was paid an examination fee of £150 subject to 20% income tax, so I received £120 in my bank account. My HMRC personal tax account shows this other university as a second employer with a tax code BR, hence the 20% tax deduction. However, I'm a higher rate taxpayer so I should pay 40% income tax on the examination fee that I received, rather than the default 20%. How can I do this in my self assessment? Thank you

Hi,

You can update this by accessing the PAYE section on the Personal Tax Account and updating your estimated income.

Thank you.