It might be a big deal... and it might not.
I would definitely e-mail iOptron immediately... and if you didn't purchase it directly from them, e-mail the vendor as well, and let iOptron know that you have done so.
I got mine from High Point Scientific one year ago, and upon first setup, I discovered a problem with the RA-axis locking mechanism. In my case, with the RA tension-adjuster knob unscrewed, if I turned the RA Gear-Switch to its "lock" position... more often than not, the locking mechanism would not engage at all. And even when it did engage, if I tried to move the RA axis, it could be rocked a few degrees, side-to-side.
I e-mailed both High Point and iOptron, and over the course of the ensuing two weeks, the problem was solved by iOptron. Fortunately, all that was needed was a longer (i.e., more powerful) spring, which was simple for me to replace, once they'd sent it to me... so I happily avoided having to send the mount to iOptron.
I have no idea what the problem might be with your Declination gear-switch locking-knob... but in communicating with iOptron, I was warned not to use any "repair" instructions that are for the ZEQ mounts, as there are some slight-but-significant differences in internal and external construction between them and the CEM25P... including the methods by which the two plastic drive-housings are attached.
Also, when you e-mail iOptron, be as specific and as detailed as possible, in your description of what the problem is. In the end, they were very helpful... but it took at least three separate communications to finally clarify the situation.
Hope your solution ends up being as overall-effortless as was mine.