how do i call a _G value from a local script?

i want to call _G.H = (mouse.hit) from a local script in a regular script by using print (Vector3.new(_G.H.X,_G.H.Y,_G.H.Z)) but it gives me the error message ServerScriptService.ChangeScript:8: attempt to index field 'H' (a nil value)

It is impossible to do so. A RemoteEvent, much less a RemoteFunction, won't help you either. Both RemoteEvents and RemoteFunctions replicate objects across the server/client boundary, and because _G can't be replicated across that boundary, you cannot transfer it to a local script from a server (normal) script. You can use _G separately on the client (it behaves the same way it behaves on the server), but you can't transfer it unless you use BindableEvents or BindableFunctions between server or local scripts.