You’ll need to have the overlay in front of your character since there is no guitar prop (which is such a shame) and animate the guitar overlay to move in accordance with the animation you use whether it’s side-to-side or up-and-down and add a loop command to it, whether it’s infinite or numbered.
If the overlay needs to be rotated and/or mirrored to fit the animation, you will need to rotate it and/or adjust the scaling with a minus value OR you can edit it and rotate it/mirror it in an editing program before uploading it to the portal, that way you won’t need to rotate it/mirror it in the actual script.
I don’t know if you’re familiar with animating overlays at all or not, but let me know if you aren’t.