How to manually add second plan to customer

Hi, I am with the following case here.

Some users did offline payments. They were already customers on the website -> they already have a subscription.

Now, I need to add more subscriptions to those users. In this website, each subscription is a different online course. None of the subscriptions are exclusive.

I tried the following process:
1. search for the actual subscription using customer name
2. clicked on customer name
3. on the user detais, there is not an option to add a new subscription, only to upgrade

How can I handle this?

Tks

Edit the user within CB > User Management and tick the checkbox next to the plan you want to give them then simply save their profile and it'll give them the subscription you selected. Registered users making a purchase is always labelled an upgrade, but if both plans are non-exclusive they'll have both plans.