how can i add extra one UDID with buid in testflight instead of making new provisional profile?
you have to edit the provisional profile in the apple development center and add the new device to it.. but you can directly update the profile through test flight (and not update the profile in xcode and re archive).
after updating the provisioning profile, you should go to your build in test flight, in the permissions tab (on the left) you'll be able to directly update the profile.. test flight will even query you if you want to sent a mail to the newly added devices (and to old ones that haven't installed it yet since last publish..).