If you signed up before Aug 9, 2021, please click Previous plans to view your applicable plans.
Go to Customers > Contacts > choose 'Unverified contacts' from the hamburger menu > check the required contacts click on 'Send activation email'.
This will send a secure link to the customer's email, which they can use to set up a password.
Alternatively, you can go to Admin > Workflows > Email Notifications > Requester notifications > toggle the user activation email ON.