Step 1. 

Log in to your Rebel account, then select "Products" in the top-left corner. In the top toolbar, you will see “Email”. Please select this. 

Step 2. 

Under Existing Cloud Email Subscriptions, on the right-hand side, there will be a "Manage subscription" button. Select this. 

Step 3. 

You will see a list of your email subscriptions there. For the one you want, select "Manage" on the right-hand side. 

Step 4. 

On the upper right-hand side you will see "Add email user", click this. 

Step 5.

A pop-up window will appear prompting you to enter the name for the email address and set a password. After filling in both fields, click "Add Email Address" to finish.