1. Provide your Apple ID
Usually at the development phase of your project, your Project Manager will request your Apple ID. This will be used to send an invitation to join our iTunes Connect group.
2. Activate iTunes Connect on a Desktop
Once you have provided your Apple ID, your Project Manager will trigger an email invitation to be sent. The sender will be "iTunes Store" so be on the lookout for that. When you receive the email, please open it on a desktop computer. I've had many clients that have reported a glitch in the mobile version of iTunes Connect. If you do not receive the invitation within 24 hours, please alert your Project Manager as invitations do expire. Once you have activated the account, your PM will be alerted, but it's always good to shoot him a text or an email letting him know you've completed this step.
3. Download the TestFlight app
On your iPhone, go to the following link and download the TestFlight App.
4. Accept Invitation to Test
When your Project Manager has seen that you have activated your iTunes Connect account, he will trigger another email invitation to be sent. Please open this email on your iPhone as there will be a direct link to downloading your app's beta inside the TestFlight app.
It's a tad roundabout, but hopefully this was a helpful guide to setting up TestFlight. Now take your time in combing through the app as you test it!