I was following some tutorial on the Roblox developer hub site, instead of having (GreenFlag.Position) it has (GreenFlag.PrimaryPart.Position) But when I add primary part in there it says PrimaryPart isn't apart of part
local zombie = game.Workspace.Zombie
local Humanoid = zombie.Humanoid
-- Variables for the points the zombie should move between
local GreenFlag = game.Workspace.GreenFlag
local PurppleFlag = game.Workspace
--Execute Script
Humanoid:MoveTo (GreenFlag.Position)

2 comments
The reach goal state of a humanoid will timeout after 8 seconds if it doesn’t reach its goal. https://developer.roblox.com/en-us/api-reference/function/Humanoid/MoveTo
Distance from point A to point B is too far for the zombie's WalkSpeed. You can use pathfinding.