From the Dashboard, click your profile icon in the top right corner, then click "Your Settings" - This will change the left navigation.

From the left navigation, click "Team" then click "Payment Method"
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You can also enter this URL:
​https://dubb.com/settings/payment-method
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This is where you can update your card on file.

NOTE: If you belong to a team, this page is only accessible to the Admin or Team Leader.