There isn't really a way to find this as applications that use the service principal do not need to register their usage, and AAD will not tell you what app has used it, just that it has been used. Unfortunately, if you have not tracked this then you will need to wait for it to expire and see what breaks.
How to find out which application is using an existing Service Principal which is about to expire.
Sachin D
21
Reputation points
We have a Azure Service Principal that was registered about a year ago by someone (probably left the organisation ). I have newly joined the team and I want to find out where this Service Principal has been used before it expires in a few days time.
From the sign in logs it show that it is being used by Storage Account but I am unable to find exactly where. appreciate if someone can help.