How to activate self-assessment option?

Hi, My wife is employed full-time and pays tax through PAYE. Her income is lower than the threshold so she has never did HMRC self assessment. In FY-2023/24 she earned some bank interest income and some foreign dividend income. HMRC has notified her to pay income tax on portion of this interest income. She estimated that her tax liability is higher than asked by HMRC. In order to pay full tax due, she tried to register for self assessment on HMRC website but doesn’t get an option to do so. She approached HMRC via online form and explained her situation and requested permission to allow her to file self assessment. It’s been almost two weeks and no response. The deadline of 31-Jan-2024 for personal self-assessment and paying tax is fast approaching. She is not sure what to do. Can you advise/help? Thanks a lot!

Hi,
Please refer to Self Assessment tax returns Registering and sending a return
Thank you.