How can I add a new UDID in Crashlytics for an existing tester? The UDID is on the distribution profile but because it's not listed in Crashlytics the user cannot open the app
You have to open the link in the invite emails on the new device. The original invite will say "Let Me In" and new build emails will say "Check It Out". Then it'll take you to the page where you can register your new device.
After the device is registered with Crashlytics you should be able to do open the app, seeing that your UDID is already in the provisioning profile.