You cant re-use an old connector, you’ll have to crimp on a new one. It may or may not be worth buying the tool/ends depending on the length of the cable.
You can buy a cable crimper and a bag of the ends on Amazon, prob for $20-$40, but if it’s just one small patch cable you’re trying to fix, you can probably buy that for $5.
I ran Ethernet through my whole house and outside for cameras, so it was worth it to me to buy the tools and spools of cable.