how to convert a normally closed curcuit to normally open
The easiest way is to probably use a NC relay, along with a small DC power supply (wall wart) appropriate to the relay’s coil voltage and current draw.

You’ll need to determine the maximum voltage and current that your NC contact is rated to handle. Also, you should add a reverse bias diode across the coil as a snubber to avoid arcing across your existing contacts.

By using a normally-closed contact on the relay, you’ll effectively invert the NC closure, turning it into an NO closure.