How do I repair a ripped song in I Tunes?

"repair"?

Please explain

If there's a problem with the audio file (won't play, has distorted or otherwise poor quality sound, etc.) there's nothing in iTunes to fix it, other than deleting the track and ripping it again from your CD. You may want to check that the error correction function for CD import is enabled, in case problems are a result of a damaged or dirty CD (some of which can be addressed or alleviated by using error correction). In some cases it may be effective to use another tool to extract audio files from the CD (Exact Audio Copyis probably the best for this) and then import the audio files into iTunes.

If that's not the problem, please post more details of what needs to be "repaired".

You're welcome. Note that there are cases where a CD may be damaged to the extent that no software can read it successfully (even though it may seem to play OK on a standalone CD player). Some CDs from a couple of decades ago suffer from "CD rot" (AFAIR this was limited to one pressing plant and a small number of labels) - discs that would be expected to look silver gradually acquire a bronze tone and may have significantly degraded playback/extraction quality. Also, there was a (thankfully) brief period when some record companies sold CDs that included a "copy protection" feature that made them impossible to rip accurately.

There is, of course, a law of diminishing returns here ... if the CD concerned is still in print (or whatever the equivalent is for online digital purchases) it may be easier to just buy a copy from the iTunes Store, Amazon, etc. rather than spending a lot of time trying to get an accurate rip 😀.