how can i make it so the player teleports to 0,50,0?

You need to make a variable to store the Player that was using the Seat before they got up. When they get off the seat, we can use their variable to move them to the respective location. It would look something like this.

workspace.Seat:GetPropertyChangedSignal("Occupant"):Connect(function(occupied)
    local Player = game.Players:GetPlayerFromCharacter(Seat.Occupant.Parent) -- We are getting the Player that is currently using the seat
    local Character = Player.Character -- We are getting their Character
    local HumanoidRootPart = Character.HumanoidRootPart -- The HumanoidRootPart is what we use to teleport the Player.
    wait(0.5)
    if not workspace.Seat.Occupant then
        Player.Character.HumanoidRootPart.CFrame = CFrame.new(0,50,0) -- We are setting the HumanoidRootPart's CFrame to (0,50,0).
    end
end)