How to increase the exposure time past 30 sec on nikon d3100?

I want to increase the exposure time past 30 seconds (I.E. 1-2 minutes or more).is there a way to do that on this camera? Please, on sure answers, no "i don't think… "

If the camera ( check your owner's manual ) has a bulb function you can but be very careful. When the sensor is running millions of electrons are passing through it creating heat. Too much heat and the sensor can be damaged and your camera becomes a paperweight.

Read page 78 in your manual.

Your max is 30s

You need to get a compatible remote for it. The D3100 is not compatible with the ML-L3 infrared remote that works with most Nikon DSLR's. With the camera in manual mode, select a speed of bulb. Set the timer mode to work with the remote. The first button push should open the shutter. The second should end it. If you never push the button a second time, the exposure will end in 30 minutes.
Start with a well charged battery. These long exposures consume a lot of charge.