Step one.
Few things are as hard as the first step. That first lift of your foot is always a heavy one.
Make it easier on yourself by making the first step just so low that you can manage to take it. Make it so that the staircase isn’t the goal, but just that first manageable step.
Because no matter what, you know that you can manage that first step. You made that step so you could get your body up there. And then you can probably manage a second one. And a third.
Always start with a step you can manage. It’s going to be so much more fun walking in stairs if you do.