There are two routes for getting Clients set up for ERC (Employee Retention Credit) and it will depend on if they are an existing Client in your My Clients section of the Portal or if they are a new Client. 

For existing Clients, simply use the Add Activity option in the Client Card, and click on Email/Document Request to send the email template that will include the ability for them to get set up. Select the "ERC Activation" template to send.  (See also: What is a Client Card?
For new Clients, you may use your Client Sign Up Page which has ERC built in. For information on accessing your Client Sign Up Page, see here: My Client Sign Up Page