Step 1:
Log in to your Seller Central account and select "User Permissions" from the "Settings" dropdown in the top right corner.
Step 2:
Scroll down the page and click the button called "Visit Manage Your Apps".
Step 3:
When you are on the "Manage your apps" page, scroll down to find "Seller Metrix" or "AMZ Analytics". If you have previously revoked the access, you will see a "Enable" button on this row.
Step 4:
After clicking the Enable button, you will be prompted to accept Amazon's terms for 3rd party developers, and you will then find your MWS Auth Token.
Step 5:
Send your new MWS Auth Token to support@sellermetrix.com and please also inform us of the email used to sign up to Seller Metrix.