how to reset the indicator symbol

recently there is a malfunction  indicator sysmbol comes on constantly on my accord car. I sent it to repair shop
two hours later I went to the shop the technician told me he reset it so the indicator is gone if the indicator comes
on again than he will replace some parts in emission control system.
Is there experienced people could tell me how to reset the indicator so that i can do it myself.
Thank you in advance.