How do I get a modulescript to edit parts from the original script?

How do I get a modulescript to edit parts from the script? Example

local module = require(workspace.module)
local part = script.Parent

module.test(part)

and in the module

function test(part)
-- code to do stuff with part from script like Part.Color = etc etc
end

It just errors to me "Attempt to call a nil value" or something