There you are. Rename that file to Help.love and you've made the standart LÖVE file, which can easily be opened in it by anyone who's got it installed!
Anyway, I made some small changes to your code.
First of all, I'm now passing the "dt" parameter to PLAYER_UPDATE and player.move: this will allow you to get a constant speed, which doesn't depend on the framerate.
Second, your old code only moved the player by 3 (and not by player.speed) if it was outside certain boundaries, but it did nothing on the inside: I changed the code so that the player has a new variable, "player.direction", which is either 1 or -1 and changes whenever you get outside the boundaries. By multiplying the speed by it, you can effectively change the direction of the player.
I'm attaching a .love file, which is just a zip file as yours with a different extension.
