how to fill form 26

This is an answer from another member from a related thread

"You must have received ARN and GST Provisional ID. Since you already received these both and created Login Name and Password, you have already completed Part B of registration. You will receive GST certificate with final GSTN Number within 3 months. Part B GST Reg 26 is for people who have not completed their process and have valid TRN Number. Email from GSTN states in following text that "if you already completed Part B, ignore this message".  We too have received this email from department."