undo, undue

Undo or undo means to reverse a job or action--
Now we'll have to undo all of the work we've already done, and start over.
In this game, you can undo the last move.

Undo may also mean to untie a string, open a package, or open a fastener of some kind--
Can you undo this bow?
He couldn't wait to undo the wrapping paper, to see what was in the box.

Undo may also mean to bring to ruin or disaster--
A story like this could undo him; we must keep it quiet.
The extortionist threatened to undo him if he doesn't pay.

Undue or undue ( rhymes with undo ) means excessive or unwarranted--
These changes could cause undue hardship to anyone who lives near the construction site.
Was he moving with undue haste when he ran into the plaintiff?

Undue may also mean inappropriate or improper--
He tends to indulge in undue familiarity; she dislikes him.
The district attorney has suggested that undue influence may have been used to suborn the jury.

Now that you know that, you can say--
"We can't undo the harm that's been done, but perhaps we can prevent any undue hardship caused by his injuries."