[Closed] Can anyone help me removing the remnants of a bolt I've drilled out the head of?

I wanted to try a single ring up front so I tried to remove the bolt. I then failed to use the right size of Torx driver and rounded it. To get round this I drilled the head off the top, but couldn't get the tread part out. No worries about using it single ring, but I've realized that an inner chainring would be a good thing, given my current status of non-fitness. Can anyone help me with this situation?