Can I clean cast iron with a steel pad
I'm not finding an exact duplicate of this question, but you should read these related questions:


Cleaning Cast Iron
Scouring pads vs. Chainmail


So, the answer to the first part of your question is yes, a Brillo pad can damage your cast iron skillet.  If you scrub it for a short time, then it can remove the seasoning from the pan.  If you scrub it really hard, it can also scratch the iron underneath, since cast iron is softer than the steel and abrasives in the Brillo pad.

In response to the second part of your question, yes, you can recover it.  How difficult this is depends on how much scouring you did.  If you just removed seasoning, you'll need to do either a light seasoning or completely reseason the pan.  If you scrubbed through the seasoning and scratched the iron itself, then you'd need to sand the bottom of the pan before completely reseasoning it.

I recommend watching Kent Rollins' video series on caring for cast iron to avoid problems in the future.