[Info] Removing trojan/rootkit from external hard drive?

Good afternoon, readers

I was curious to find out how it might be possible to remove a computer virus (I don't know if it is a rootkit or trojan) from an external hard drive without re-infecting my own computer. I say I don't know which it is because when I ran a scan previously with my computer, I'd "find" an infected item called "SVC.host" and I'd remove it. (Yes -- I know there is a good SVC.host for processing)

It originally came from my computer when I plugged it in trying to back up some important items; I hadn't processed I'd be backing up my issue with me!

I ended up getting my computer fixed, thus not having to reformat. So I don't believe that I need that backup I created. However, I fear I tread thin ice in possibly re-infecting my system.

Help?

Thank you in advance,
A.

Alright, I've downloaded, installed and immunized my computer with BitDefender.
What's next?
I assume I am going to plug in my external and "immunize" it as well with BitDefender?

Alright, once I do that, what would you recommend using to scan for viruses and cleaning up? Malwarebytes?

Thanks a lot, Broni!
This is the second time you've pulled me from the pickle jar.

Many thanks,
A.