The AWS Well-Architected Tool is in the AWS Console. You simply need to login to the console and navigate to the tool.
Sign in to the AWS Management Console as an IAM user with MFA enabled or in a federated Role, and open the Well-Architected console at https://console.aws.amazon.com/wellarchitected/.
If you are already in the console, click Services on the tool bar along the top of the console to bring up the service search. Start typing Well Architected into the search box and select the AWS Well-Architected Tool: