A very common way of sharing iOS builds is through TestFlight. Generally, these will be set up as shared accounts. This article goes through the process of how you access those shared accounts and some best practices as well.
For iOS 13 users, if you are unable to sign out of the Apple ID (the username is greyed out) scroll down to "For iOS 13 users" to fix this issue.
1. When you are in a project the EM will most likely have added the TestFlight credentials to the project, which can be found by either:
a) Checking the Project Details
b) Checking the Run Details
2. When you are ready to test, you need to log into the TestFlight account on the iOS device that you have been assigned.
a) How to do this:
Go To Settings -> Tap on the first option to access your account settings -> “iTunes & App Store” -> “Apple ID: (existing email)” -> Sign Out
3. Download the build for testing, and complete your testing task
4. When finished, sign out.
a) Don’t redeem any codes on a shared account!
b) Don’t download any other apps on the shared account!
For iOS 13 users:
1. Go to Settings -> Tap on Screen Time -> Tap on Content & Privacy Restrictions
2. Notice the Content & Privacy Restrictions toggle has been turned OFF, turn this toggle to ON
3. After the Content & Privacy Restrictions toggle has been turned back ON, you will be able to select your Apple ID and log out to sign in with the appropriate test credentials
Please note: There is usually a delay when signing in and out of the Apple ID. Once you sign back into your personal Apple ID the account may not be selectable immediately. If you wait a little while, it will be able to be selected again as described in the instructions above.