First, head over to your Google Analytics property.
Click on "Admin" in the lower right corner:
Next up, you need to select "Property Access Management" under your property settings.
Here you can add new users or add the rights of existing users. You can add new users by pressing the blue + button, and you can alter the permissions by clicking on the three dots next to a name and then clicking on "view users account details".
After clicking on either the plus button to add a new user or the three dots to alter the user's permissions, ensure the user gets "Edit" rights.
After this action has been performed, the user in question can connect the dimensions in the Google Analytics integration within Datatrics.