Pilot reported approach controller issued a low altitude alert during IFR approach to land.

Narrative

While conducting the ILS approach to Runway 31 at DSM I received a low altitude alert from the Approach Controller; was instructed to climb to 2500 ft. I did so; intercepted the glideslope and made a normal landing.I was cleared to and cross CYCLN (IAF) at or above 3000 ft.; cleared for the ILS 31 approach. Hand flying (no AP) I descended to 3000 ft.; flew direct to CYCLN; turned right to join the localizer. I crossed over CYCLN and descended to the next lower altitude of 2400 ft. until FOREM (FAF). At 2400 ft. I was above the broken cloud layer; I had Ground contact at this time; the layer appeared to be thin. My localizer needle bounced full left then right then slightly left indicating I was slightly right of the localizer centerline; while confirming the Garmin 430 non WAAS was in the correct mode (I had previously confirmed this but was taken back by the needle bounce) I simultaneously accidentally pulled my approach plate and airport diagram off the yoke clip (I'm old school and prefer paper as opposed to iPad) spent several seconds looking between my legs for it; finally retrieved it off the floor; started correcting to the left. The Controller issued a 'low altitude alert' and instructed me to climb to 2500 ft. until established on the localizer. At this time; I was at 2000 ft.; I immediately climbed to 2500 ft.; course corrected slightly left; became established on the localizer; intercepted the glide slope; handed off to Tower and made a normal on course stabilized approach; I broke out with good visibility (2-3 miles) just as I passed FOREM around 1200 ft. agl; landed normally.Altitude deviation due to last minute troubleshooting the radio setup and bending down to floor to find lost papers resulted in forward pressure on yoke and resulted in a descent.