I do think the wrench BB81 shows you should be in your kit. It is the 36mm needed for the top nut and also fits the fork legs at the bottom too. The collection of tools known as the on board tool kit is what ever you say it is. Get whatever tools you need. Have two tool rolls. You don't have to have tools in a tool roll anyway. But you need all the need tools.
Take those barbacks off and you can then slip the hook wrench under the top clamp to feel if the slotted nut is there. Because you don't know what I'm talking about really and won't know what that is so the next step is to take the top clamp off. To do this remove what ever else is in the way and use the pin wrench, yeah, you have that one, and take #s 5 thru # 10 off. Both sides. Under the top clamp is the slotted nut.