game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = + 20
First of all, I'm not sure if you can do =+ in Lua, I think you might need to actually say
game.Players.LocalPlayer.Character.Humanoid.WalkSpeed=game.Players.LocalPlayer.Character.Humanoid.WalkSpeed + 20
Also, this needs to be run in a LocalScript, or else LocalPlayer cannot be defined. I can't help you other than that without any output.
-- Leave a +1 Rep if I helped <3
Oh! That is so easy, If you want to do it my way, Just use this code I dont know how to find the player, So lets just say your player.
game.Players.MrGameMasters1.Character.Humanoid.Walkspeed = game.Players.MrGameMasters1.Character.Humanoid.Walkspeed + 20
(Not Copied, I just thought no one would answer, Used in a script, not in a localscript Unless your using localplayer) Tell me if it works, If not, Change Humanoid To Humaniod, Cause i might've got it wrong