Welcome to the community, Swapnil Tripathi!
If you want to convert your internal into an external, you will need to get an external enclosure for it or a dock station. Just make sure it is compatible with a 2.5" inch drive. Google should be your friend here and show you various options of those.
Once connected and your external drive is working, you can plug it in your computer and pull any files you want from it.
The next thing I'd recommend is to format the drive and start with a clean slate.
You should be able to retrieve your old files and after reformatting the drive, you can use it however you please.
Hope this helped.
SuperSoph_WD