Navigate to your GTM account and click on the container name that you wish to grant access.
On the top-left side of your screen, select Admin.
Once you are on the Admin page, in the Account column, select User Management.
From the top-right corner of your screen, click on the "+" sign and select Add Users.
Enter one or more email addresses to send an invite and click on the container you want to give access to under Container Permissions.
A side panel will open and here you need to select the Publish permission. When you click on Done, the side panel will disappear. Finally, click on Invite.