Find your exisiting username/password through the Heroku portal :

If you are a Heroku user using the SendGrid add-on, and would like to access the SendGrid web interface, or would just like to know your Sendgrid account credentials; you can find them by doing the following from the Heroku interface:

  1. Go to your Apps, choose Sendgrid
  2. Click on “settings” and then click “reveal config vars”

Reset your SendGrid add-on password:

Go to the Password Reset page and enter your SendGrid username, and click submit. An email will be sent to the email address on file with instructions on how to reset your password. If you don’t know your SendGrid username, use the steps detailed above to find your username through the Heroku portal. Keep in mind that resetting your Sendgrid password may break any integrations you have that are currently using the exisiting credentials for authentication.

Alternatively, you can contact Heroku Support directly to request a password reset for the SendGrid add-on.