You normally can’t move the slider’s arrows, but I think you should be able to recreate a functioning slider with what has been said in that topic. Even in the template you found, it doesn’t work.
I think you will have to recreate the slider from scratch since the real arrows have been deleted in your template.
EDIT: My bad, you can in fact move the arrows with absolute position, which is simpler than the solution I shared. Thanks to Stan