Is he on leash when going up and down the first level? If he is, does he just refuse to go on?
We live about 50% of the time in our motorhome. Of necessity, we have taught our 4 m/o Pyr/malamute mix pup to go up and down the steps. I just couldn't carry him any more. (I can still pick him up, but felt very unsafe going up and down steps with him.) I do know that going up and down steps in general isn't good for a growing pup, but had no choice in this.
How we did it: first of all, he's on leash. (He's actually almost always on leash right now, as it is the best way to keep track of where he is, and allows us to supervise him better. We keep him near us at all times)
Second, I used treats to keep him interested in going down. Lots of encouragement and praise too! One step at a time, and I sort of supported him to keep him from stumbling and falling down. Going up, I used treats again, placing them on each step, and assisting him in getting started. I can lift him up the first step, to get him started, with his front feet on the step, and then I lift his rear end.
We just worked on it little by little. He does them well now, well enough anyway, and we still support him and stay close, because being a puppy, his feet get in his way sometimes.

We don't want him to trip or stumble, and fall.
So, we stay right close, use treats, take it one step at a time. I DO NOT expect him, nor want him, to BOUND up or down right now. Just don't want to injure him; this works well enough. The only thing we had to do was find a way for him to get in and out of the motorhome without having to carry him. And to do it safely.
Good luck.