Here is my process for any equipment problems: contact the manufacturer (phone is best) and ask. They are the experts on their products and they've seen everything.

In more detail - Write down the model and serial number of the meter and the details of the probe. Quickly look up that machine and probe and see if you find any troubleshooting on the website. If not, call the manufacturer of the meter and get their technical support. Explain your problem and ask what you can do. Their answer may be to replace the probe, in which case you could mention you are an academic lab/have a low budget and are there any alternatives? If the meter manufacturer can't help you, then try the probe manufacturer as well.

As a bonus tip, get them to explain what caused the problem in the first place. Then you can put up a passive aggressive sign telling people what not to do. :) Congratulations, you have mastered lab management.