بسم الله الرحمن الرحيم
In the question mentioned above that five hundred note is unclaimed stuff. If you have picked it up then safeguard it and keep on enquiring about its owner. If you get the owner then hand it over to him and if you don’t find the owner and you have no hope of finding him then give it in charity to any poor.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.