Try to make a script disabling the main animation script in the character, copy the original animation script and then paste in the StarterCharacterScripts, change the walking and running running animations to your animations (inside the scripts and in the animations.
In the animation editor change one of the settings to looped. Here’s a link that should help you with the animation editor, this also explains in more detail on how to loop and things like that. Animation Editor | Documentation - Roblox Creator Hub
You need to fork the Animate script of the Character and have it replace the Player’s Default one. Simply modifying those properties won’t fix your problem.