I think the only way is to remove the instrument cluster, and see if it can be disassembled from the back side. It may be something you can take apart without damage, or maybe not.

If you do, I suggest you make a template showing where all the screws or bolts are in the back of the cluster. The heads look identical, but the threads are different. The screws just hold things together. The bolts make electrical connections.

For my '88 760, I used a piece of corrogated cardboard, traced the cluster outline, diagrammed each screw/bolt head location, and pushed each one into its position on the cardboard as I removed it. Mixing up scews and bolts is supposed to cause weird gauge cluster misbehavior.

But before you get to the backside, you have to get the cluster out. My '88 has screws holding the cluster into position in the air vents on either side, along the bottom, and a couple hidden behind plastic covers in the upper inside part. Remove all you can find, tug gently, and look for another screw where it doesn't want to come loose.

OTH, just ignore it. The plug shouldn't do any harm sitting inside the clear plastic cover. And 99.999% of the rest of us will never notice.