THIS FILE MUST HAVE THAT SYNTAXIS:

if not Metrostroi.Skins then Metrostroi.Skins = {} end
if not Metrostroi.Skins["ezh3"] then Metrostroi.Skins["ezh3"] = {} end
table.insert(Metrostroi.Skins["ezh3"],{
	name = "Green-Blue",
	path = "metrostroi_skins/ezh3/1",
})

WHERE:
table.insert(Metrostroi.Skins["ezh3"],{
	name = "Green-Blue",
	path = "metrostroi_skins/ezh3/1",
})

YOUR SKIN
table.insert(Metrostroi.Skins["type of train(ezh3 or 717)"],{
name = "YOUR NAME"
path = "PATH_TO_VMT_AND_VTF",
})