I’ve been using Cubase for years, but still haven’t used all of the great features, but I am trying. Here’s my problem, one of my instrument tracks has a high pitched, distracting ringing that occurs frequently. I am sure it is within the nature of the instrument. But, I would like to dampen that ring, but I don’t know what tool will do this. I’ve tried eq, and a couple of other things, but because I am not very good at using those inserts, yet, I don’t know what I am doing.
Even if you need to give me a metaphorical eye roll, please help me, if you can. I would sure appreciate it. Thanks 
No eye rolling necessary. A good start would be to tell us what the name of the offending plug-in is and a brief description of your O/S and version of Cubase.
I’m interested in what can be done about this as well. In my case, it’s a digital hi-end ringing that was traced to cheap VSTis. It’s like digital dirt. My work-around has been to adjust the amp and filter envelopes. The filter envelope maximum can be lowered to reduce the offending sound in general. (EQ has limited repressive powers, and often damages the timbre too much). Since the problem is more noticeable on the decay, it really helps to shorten the amp envelope decay time. I’ve found in necessary to shorten the filter decay time to just slightly longer than the amp envelope decay time in order to keep things sounding credible. If there’s too much damage to the high end, I’ll layer in another patch to cover the lost spectrum. Naturally, the high end grafted patch has to be free of digital dirt. Sometimes I might convert a patch that wasn’t designed as a primarily high end sound into a candidate by filtering its low end away. (Morphing filter is often promising for that.)
Anyway, I’d like to know what others are doing if they encounter this sort of problem.
Could this be a trial VST whose trial period is past. These are typically programmed to play a recurring noise for a few seconds every 30 seconds (or some other repeating frequency) until you purchase the full license that unlocks the trial.
Regards. 
EQ usually works well for things like this. Basically it is a two step process & the 1st step can initially seem a bit counter-intuitive.
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First you need to figure out the offending frequency. Start by setting the Q control to a high value (high values affect a narrow band of frequencies & low values a broad band) and the Gain to boost the signal by a fairly large amount (+8dB maybe more). This will all sound pretty bad. Now sweep the Frequency until you find the spot where the ringing sounds the worst. That’s the frequency you want to tame. You might want to take a short break at this point so your ears forget this nasty exaggerated sound.
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Next you want to cut this frequency. Set the Gain to 0dB and the Q to a modest value (~0.8). Slowly reduce the Gain until the ringing sound is less pronounced. Listen carefully while doing this, you might need to adjust the Q to narrow or widen the band around the frequency to achieve the best results (typically in the range of 0.6 to 1.2, but outside that is also fine if needed).
Starting off this whole thing can take longer than you’d like. But as you gain experience it gets a lot quicker.