How to make only team helmets and how to make them wearable?

I already answered your other question, you probably didn't see it but now I know exactly what your looking for.

local Hat = 42 -- put helmet assetID / hat ID here

local Players = game:GetService("Players")
local InsertService = game:GetService("InsertService")

local function AddHelmet(Player)
   Player.CharacterAdded:Connect(function(Character)
   wait()

     local Team = Player.Team
     local TeamColor = Player.TeamColor

-- you can find the team TWO ways, using the name, or the color! Change them as you want.
        if Team.Name == "TEAM NAME" or TeamColor == Color3.fromRGB(0,0,0) then
          InsertService:LoadAsset(Hat):GetChildren()[1].Parent = Character
        end

   end)
end

Players.PlayerAdded:Connect(AddHelmet)