Welcome to the forum!
Click the little green pencil pad button in the top corner to edit a wiki post (you can create those once you're at the trust level regular!), but I think since you're a basic user, you can't. :0
Unlock the trust level member, and then you can edit wiki posts! :D
You can also click the three dots at the bottom of the wiki post, and click the pencil. :D
If you want to edit your own post, then tap the little pencil near the like button, once you've finished editing, save the edit (with the little Aqua button in the bottom left corner!)! :D
You can edit your own posts anytime, unless a few months have passed. :D