The job description of the bank courier at least requires a high school diploma institute. You might think that the training is provided on the job then why there is a requirement of diploma. It is to make sure you pass the basic cut-off bar set by the recruitment companies and you are eligible to apply for the job. Moreover, learning communication skills requires a thorough experience that can only be gained at the school.
You must acquire a driving license and should have a clean record as well. You will be driving from places to places to deliver the documents, hence, you should be able to prove yourself as a careful driver and not dangerous that can put the bank at risk.
You should know the area of your work that you will be dealing in and try to understand the main purpose of that department. If you will know the in and out of the department, you will be able to make crunch decisions when you lose route and deliver the documents on time. You have to prove that you are reliable and not careless.
Join a computer course where you can enhance your computing skills if you are unaware of how to use Microsoft office and other simple tools in the computer because that will be a plus point for you especially dealing in administrative tasks.
Apply for the vacant positions.