the recommendation above is like a magnafier,, you can also buy screw on filters doing the same. they do work, but create very narrow depth of field, but quick way of getting closeups..
Also,, not sure if your camera even in manual mode can use an old manual lens. yes, I know the light meter won't work, but I wonder if the camera will snap,, when set to manual mode. one can always take a few test shots, dialing in the exposure,, (looking at the historygram), and then shoot.
reason.. the old 55 macro lens are gems and can be purchased for less than 100 dollars.
but again,, I do not know for certain if your 3100 will not lock up with that lens on.