How can I change walk animation after I turn on animation script?

As you see in title, I have to change walk motion while animation is already deployed(or animation script is running). How can I change it so I can make it with out error?

I dont know whats the problem, but you can stop playing 1 animation and start playing another This will help i think

https://developer.roblox.com/en-us/api-reference/function/AnimationTrack/Stop