[Koha-devel] need help in joining date for the patrons

Hello, I am working in a library with computer science back ground and new to koha. I donot know much about it. I need help in joining date of patrons . when i add a patron i do not give the joining date of the person. then i edit this patron, in edit page the joining date of this person is not displayed (today / current date) and i cannot add its joining date again. i want to edit the joining date of the patron how can i do it . Why it is not showing the date, if i give the joining date when adding a new patron. Regards, Zahid