The easiest way to add a link membership dashboard is via an App Embed. This is a special widget that you enable within your Shopify theme that will attempt to add a membership dashboard link to your customer account page.
You can access the App Embed directly by clicking the button on the Installation tab of your membership details page.
If you feel comfortable editing HTML and would prefer to add the membership management link manually, you can edit your Shopify theme directly. To begin, head to your Shopify's Online Store section, and click Actions > Edit Code next to your theme.
Select the customers/account.liquid file from the left hand menu.
Find the spot on this page where you want to include your Manage Membership link. Paste the code there. The code can be found on Subscribfy app admin Installation page on STEP 3.