You cannot perform any sensitive transactions because your cellphone number is not activated for SMS Authorisation

I can never do anything on my online banking because I always get this message:

You cannot perform any sensitive transactions because your cellphone number is not activated for SMS Authorisation.

In order to do sensitive transactions, please visit your nearest branch to re-activate SMS Authorization. If you have any queries contact ***or+***0.

Who deactivated it in the 1st place? Is there another way to reactivate it because I am not willing to go into a branch given the pandemic.