Situation 1 : Add the payment method on the member profile from the manager side

Go to the member's profile -> under Payment method click on Add a payment method

Situation 2: Ask your member to add their payment method

Go to the member's profile -> under Payment Method click on Copy the link to add a payment method.

Go to the member's profile -> Click on the envelope -> New email -> Write your email and paste the link to add a payment method -> Send the email

By clicking on this link your member will be automatically redirected to a page in their member profile where they will be asked to add a payment method. Use this link after the migration of your data to ask your members to fill in their payment method for all future subscriptions.