I was wondering if there could be a button where we could click to grant edit access to other users, like if you wanted to work on an article together

Since wikiHow is (obviously) a wiki, generally anyone can edit any article at any time. So unless the article is protected in that only admins can edit it or an editor is blocked from contributing, there is no system of granting editing access to specific individuals. 

I would suggest putting an in use tag on the article in question which will request that no one edit the article temporarily, then work on it together within the 2 week time period.

Hope this helps!

Thanks!

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