Hi,
By default leaves go to the manager and HR Manager for approval, you can refer below links on how you can setup a reporting manager and delegate HR Manager rights to people:
https://docs.uknowva.com/how-to/106-how-to-set-a-reporting-manager-of-any-user-in-uknowva
https://docs.uknowva.com/how-to/hrms/157-how-to-delegate-hr-manager-rights-in-uknowva-hrms
Let me know if that helps.