Mine are yellowing as well. They ran the course & it's been a long hot summer. Now, it's sleepy time. They don't want food & only rain water. Just let them whittle down & go dormant.

as Bathgate says at his time of year it is just the plant settling down for winter. the plant is reabsorbing the chemicals to make the green chlorophyll for next year. the yellow is the remaining pigments left behind. let the plant die back. remove the leaves when they have 'flopped' and often they go mushy.
are they in a pot or the ground? if in a pot keep it frost free before repotting the corm/tuber next spring. if in the ground then leave it as it is.