STEP 1: Go to your YouTube account and go to the upper right hand corner where your profile photo is.
STEP 2: Choose YouTube Studio / Creator Studio section of your YouTube Channel
You will need to log in using your Gmail account associated with the account.
When adding a user, you have add someone else by their Gmail as well.
(unfortunately Google Apps for Work/GSuite emails do not always work!)
STEP 3: On the bottom left-hand corner, click Settings
STEP 4: A pop up will appear. On Left hand margin, choose PERMISSIONS