Before I changed my address to my Thai address, I asked a question via online banking. I told them I was thinking of moving to Thailand permanently and asked if I could still operate my account and credit/debit cards with a foreign address. After HSBC confirmed that I could use my account & cards as normal, I changed to my Thai address, even though I had ALREADY moved to Thailand permanently.
I did receive an lndividual Tax Residency Self-Certification Form to complete from HSBC. I had to declare my country of residence and disclose my Thai Taxpayer ldentification Number. I don't have a TIN so I replied saying that my visa (extension) prohibited any kind of work and had no Thailand income, so I didn't have/need a TIN. This was accepted by HSBC.
I didn't encounter any problems setting up the HSBC app, including the digital secure key. You can also enable biometrics to log into the app (assuming you have a compatible phone).