Tab Order

I created some custom fields for user profile and for postings.
For example when you goto https://www.bharathrentals.com/wp-login.php?action=register to register

You click on username and enter username and hit tab
it goes to the next field email and so on
But when you are in A few words about me and enter something and hit tab, it does not go to the next field (mobile country code – my custom field); it goes to the submit button

how to fix this?
thanks