The bank . . . . . . . . at 9.30 every morning from Monday to Friday.

Both 'open' and 'opens' are correct but depends on sentence and subject line.
For example "He opens the door," that is correct.
"Door is open," that is correct if only one door if more than one door is open then use "doors are open"
Open is singular form but opens is plural form.
In the given question 'opens' is the right usage.