Learn how to easily add marketplaces via the tool in this article.
Step 1: Open the account settings.
Step 2: Click on Amazon Connection.
Step 3: Now select Add missing marketplaces under seller central or vendor central (depending on which marketplace you want to add).
Note: As new marketplaces become available, they will appear in this view.
Step 4: Select the desired marketplaces and confirm your selection with "Add marketplaces".