Speed and Jump boost script wont work?

In my game, you get get different souls that do different things. When the player equips this soul, its supposed to increase the players jump power and walk speed, but it wont work

(its a normal script located in StarterPlayerScripts)

local IntTrue = game.Players.LocalPlayer.SelectedSOUL.Value.Name == "Integrity"

if IntTrue then 

script.Parent.HumanoidRootPart.Humanoid.WalkSpeed = script.Parent.HumanoidRootPartHumanoid.WalkSpeed + 90
script.Parent.HumanoidRootPartHumanoid.JumpPower = script.Parent.HumanoidRootPartHumanoid.JumpPower + 90

end

But it wont work. do i have to make it a local script? or is something wrong with my code?

the output error is: 15:29:43.946 - Workspace.trimarkander.Script:1: attempt to index nil with 'SelectedSOUL'

(P.S. im new to scripting, so sorry if im really dumb rn)

Here is what is wrong:

Instead of doing

script.Parent.Humanoid.WalkSpeed + 10
script.Parent.Humanoid.JumpPower + 10

try

script.Parent.Humanoid.WalkSpeed = script.Parent.Humanoid.WalkSpeed + 10
script.Parent.Humanoid.JumpPower = script.Parent.Humanoid.JumpPower + 10

The reason why is because it is taking the current value of the player, and adds 10. You cant solve math without an =