Are you asking how to get your wiki onto the Fandom app? Unfortunately, I can't find the page that describes the process; perhaps it got deleted. Basically, you need to contact staff and request to be added. Staff will then evaluate your wiki for "mobile readiness" and will add it if your wiki is ready and large enough.
It is possible to create a wiki on mobile, I just tested that on my phone. Except that in some mobile browsers the "Start a Wiki" button will not appear, so you have to type the Wiki creation URL into the browser URL.
And that's what I had to do.
If you are using the app, I don't think you can. However, if you are using a mobile web browser, then you should be able to do as Jonky555 said. However, you may need to switch to desktop view first as well.