Hi @Anonymous,
Do you want the Office 365 Admin have full permission to approve/reject an approval request sent to any Employee within the Office 365 group?
If you want the Office 365 Admin to approve/reject the Approval request when the Employee doesn't make a response to the Approval request within specific time, I think @ScottShearer's solution could achieve your needs.
If you want the Office 365 Admin have full permission to approve/reject an approval request sent to any Employee within the Office 365 group no matter if the Employee has made a response to the Approval request, I afraid that there is no way to achieve your needs in Microsoft Flow currently.
If you would like this feature to be added in Microsoft Flow, please submit an idea to Flow Ideas Forum:
https://powerusers.microsoft.com/t5/Flow-Ideas/idb-p/FlowIdeas
Best regards,
Kris