Please note, that before you watch the video below, it is essentially to note the information below is required.
Please ensure you add the following email address (inside the yellow box below) as an App Manager role within your account and ensure that the manage certificates checkbox is marked too.
If for some reason you are unable to check the box for managing certificates, please check to ensure that you have an Organisation developer account and not an Individual developer account. If you have an individual account, you will need to change this to an Organisation account before you can complete the video below.
As part of that process you will need to obtain a D-U-N-S number which you can see how to get in the tutorial lower on this page. To change your account type, you will need to contact Apple support and request that change to be made.