best game to get him worked up. you can gently pull him up onto the first step.
as soon as he gets to the first step, let go of the toy so he wins the game. the joy of winning will completely distract him from the fact he just climbed up a step. give him lots of verbal praise and cuddle him too.
now carry him back down the step and continue to play around again. you’re going to build his confidence up very slowly. if he’s young he may be particularly nervous so you don’t want to rush training.
now using play, lead him up the second step. again, tug of war 