For setting up the membership subscription form, you will have to copy its HTML code from the app dashboard and add/paste in your theme where ever you want to show it. To add it in a page, follow below steps –
Step 1. After creating a membership plan, either navigate to Dashboard or Plans. Then, click on the Get HTML code link in the dropdown of the settings button.
Step 2. Copy that code and from Shopify dashboard, navigate to Online stores > Pages. Now either add a new page or open an existing page where the form is required.
Step 3. After that, click on the icon “<>” for HTML editor, paste the copied code and Save.