How to let character move along a specific path?

Hi everyone, I wish to use Spline to create a specific path for my character.
It’s like a footbridge, I don’t want my player to move left or right, just forward or backward.
I’ve searched a lot of tutorials about Spline, but all of them are about auto-move. I wish to let player could still control the movement.
Does anyone know how to do that? Or send me a tutorial link about it?
Thank you soooo much!!