How to write a letter to the bank manager to issue me a credit card?

Bank Managers have nothing what so ever to do with deciding who gets a credit card and who doe's not.

This decision is made by the credit department of the bank issuing the credit cards and will be based on your application and credit report.

As long as your score, income, debt to income, debt to credit, payment history, time in bureau, time on job/at residence etc. meets their guidelines you should get your card.

when applying for credit card its not up to any bank manager its up to the credit reporting agencies

they don't have any say in what so ever

the credit card companies check your credit report

see if you have outstanding debit or have you paid on time how long you have lived in the same place

how long have you been employed (self employment might harded to prove)

how much income you get coming in etc

If you have a business, you are better off establishing business credit. www.BusinessCreditKey.com - worked very well for me and showed me how to establish business credit without using personal credit

This is a great question