Setting Animation Progress
JavaScript can be used to change how far an DOM element is into its animation by changing its animation-delay property.
If this is negative, then the animation will start out as if that amount of time has already passed.
E.g. animation-delay: -2s; will style an element as how it would look 2 seconds after the start of the animation.
If what you want to do is the sensible thing of setting a percentage progress through the animation, then you'll need to multiply that percentage by the animation duration.
animation-delay: calc(-1 * --animation-progress * --animation-duration);
Resetting Animation Progress
To put an element back to its position from when the page was loaded, setting animation-delay: 0; won't necessarily work as it may have started out with a delay.
Instead, you can remove the CSS class/id that provides the animation from the element, access a property on it that triggers reflow, then add the class/id back in.