In the given situation the appropriate step would be to give sets of 5 back slaps and 5 chest thrusts.
If one finds an infant choking, and he or she is not responding, then first kneel or sit with the infant in the lap. Hold the infant with the face down and resting on the forearm, with the head slightly lower in comparison to the chest. After that, there is a need to apply 5 sets of back slaps and 5 sets of chest thrust.
Clearing a substance from a responsive infant's airway needs a combination of chest thrusts and back slaps. However, abdominal thrusts would not be appropriate.