I want to update the contact in ActiveTrail when he joined the group with a different value for each contact

Hello

I want to create a bulk username and password for my SaaS platform and use it to send them to new customers who register in my ActiveTrail form.

I created a Zap with this automation
Contact Added to Group in ActiveTrail >>> Create/Update Contact in ActiveTrail
I set under username the value: user1. under password: pas1
and it works well.
But how can I use a different value for each contact?
If I set on username the value: user1, user2, user3
this is what I get in the contact card (see image attached)