Relink an Account within your Product
When one of your customers goes through the Merge Linking Flow for the first time, an end_user_origin_id should be created for that organization. You should store that value in your backend, so that when the customer comes back to the linking flow to update their credentials, you can initiate the relinking flow, rather than create a completely new Linked Account.
To relink an account, and to prevent creating a new one, you will need to pass the existing account's end_user_origin_id to the /link-token endpoint. That way when the existing end user opens Merge Link and a new link token is generated, Merge will recognize them and ask for updated credentials to their account instead of setting up a new account.
Relink an Account using Magic Link (Send Link via URL)
You can initiate a relinking flow through Magic Link! This would be done by going to your Production Linked Accounts page within the dashboard and clicking on "Send Link via URL".
It would be a similar process, where you will need to pass in the same information used to create the account as part of the Link URL set up. The Unique Identifier would be where you input the existing end_user_origin_id, and you can pass the similar existing information accordingly. From there, when the end-user opens Magic Link, they'll enter the relinking flow.