After a user logs in they will arrive at Purchased Products where it will list their products. From here they will need to find the SendGrid app. Below is a step by step screenshot of how to locate the password section so that they can update their credentials.
From the Purchased Products section select SendGrid on the left hand side of the application block.
After selecting the link you’ll be in the Manage Product page specific to SendGrid:
From here you can select the Settings tab which will display the below information. From here, you can reset your password for SendGrid. Please keep in mind this is for the parent access and not subuser access that may have been added via the SendGrid UI.