A
may help people give acurate advice, but here's my go from what you have said.
If there is mushy parts on the roots you need to cut those away or they may spread.
Don't make the mistake I did to then use Cinnomon on the wounds. There is a lot of talk on this group that cinnomon is good for wounds on orchids, and it IS, just not good for the roots as I found out later.
I'm not sure if a quick rince in Listerine is good for roots or not, maybe someone else can say if you need to do anything like that after trimming the roots.
Once the roots are trimmed you then need to see how much of the roots are left and are good. If there are plenty of good roots left then I would advice just potting it back up and careing for it as normal.
If you then have hardly any roots left (if any at all) then you may need to try something like 'Sphag n Bag'. I can't find the link just now maybe someone else knows where it is or maybe you can find it with a search of this site.