This picture is to guide you

While editing your guide, you should be seeing something similar to this.

Guide type should be "Champion"
Instead of the Aatrox icon you should select the Vayne icon
Choose map should be according to your guide, which is Summoner's Rift
Team Role and Lane are changed accordingly

I hope this helps

Great, albeit overused, pun but the title makes no sense this way. Thought you should know.

how do i make it a champ guide? every time i try to change it, it automatically switches to general

Why not make it a champion guide instead of a general guide? You miss out on the cheat sheet which is very important for the guide itself.