You say you can connect to the drone's wifi? Then you're almost there. It sounds like you just need the APP. Tell us what kind of drone it is (A.R.?, Bebop?, Bebop 2?) and we can help you find the app to fly it. If it's from a garage sale, my guess is it's not an Anafl.
Parrot A.R drones use the "AR FreeFlight" APP- It's no longer in APP stores. Someone here may still have an APK file to install it.... I think I have an old copy.
Bebops (both models) use "FreeFlight Pro". Then there are the 3rd party apps like "Bebop Pro" you might use... If it is a Bebop, there are still several apps available to fly it in your phone's app store. Apple offers the original "FreeFlight Pro" and "Bebop Pro". Note: "FreeFlight 6" is strictly for the Parrot Anafli. Be sure the app you download is for the model you have....