What is wrong? What is it made of?
Paula....We need a little more info concerning your problem.
Here's a tutorial that might help: https://www.hometips.com/diy-how-to/door-threshold-install-replace.html
Some thresholds have adjustment screws on the top. These raise and lower the threshold so that it fits better
What part of the threshold is damaged?
Inside or outside. Any pictures would help!
Thresholds at your local home improvement store aren't terribly expensive. That may be a better way to go than trying to repair it.