You definitely can't customize the -capabilities- of the About box - at best you could put in a link directing users where to go to complete the form that you've hosted elsewhere. Note that the About box does support markdown, so it might even be possible to embed the link as an actual hyperlink, but I've not tried that.
As an alternative, perhaps you could offer the needed functionality into the app itself. E.g. if you have a tab, put something in the footer for example.
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