How to Anchor player?

Simple enough. You would simply just create a LocalScript and put this script inside a gui, or just in the game.StarterGui instance as is.

The Code With Helpful Notes

local player = game.Players.LocalPlayer --Getting our player
repeat wait() until player.Character --Making sure our character has fully loaded
local char = player.Character --After it's loaded it will set this variable
local head = char:WaitForChild('Head') --Getting the head from our character

head.Anchored = true --Making the characters head, anchored. 

Hope this helped! If this answered your question please accept my answer!

local L_1_ = game.Players.LocalPlayer --Getting our player
repeat
    wait()
until L_1_.Character --Making sure our character has fully loaded
local L_2_ = L_1_.Character --After it's loaded it will set this variable
local L_3_ = L_2_:WaitForChild('Head') --Getting the head from our character

L_3_.Anchored = true