WHAT QUALIFICATION FOR I T RETURN WORK ?

You can work on ground level, but can't represent in department. Well, additional certificate as Tax Return Preparer (TRP) will be beneficial.

WHAT IS PROCESSES FOR TRP CERTIFICATE ?

You can get all the details at https://www.trpscheme.com/

Good luck.

CAN WE PAY TAX ONLINE FROM THIRD PARTY BANK A/C IF RETURN FILE PERSON HAS NO ONLINE BANK A/C ?

Third Party! From your own account payment can be made on behalf of your client, which he reimburses when billed.