Coolant temperature gauge on dash showing wrong temperature while ECT reads correctly.

Now that I see it, the only way I can think of to correct it is to take the IPC out and take the faceplate off.

You might be able to get away with just rotating the needle clockwise to the C, but if not, then you'll need to pop the needle off the shaft and then reinstall it.

There is a bit of trim to remove to get to the IPC, but once you can access it, it's pretty easy to remove: 4 screws and 1 plug.

Here is the thread where I share swapping my IPC from white to red LEDs.

Gen7 Instrument Cluster Innards | Chevrolet Malibu Forums (chevymalibuforum.com)

I will wager that it's an issue with the needle, or even more the gauge's little motor, that allows it to swing past the range markings.

When it's off, it should rest below C, and when it first starts, all of the gauges make a full sweep and then return to their proper places. If it's not going to C, then there may be some schmutz interfering with its movement, or the needle has somehow moved, but I think that's very unlikely.