Add approvers to self service generic approval process

Hello, we're currently using Oracle EBS 12.1.3.

I'm trying to figure out how to add approvers to a certain step in our self service leave workflow. Currently, if the leave application is not approved by the manager in 2 days, it goes to a specific person in HR. I would like to add more performers to that activity step in the approval process. Can anyone provide some guidance on where this is done?

thank you