In the standard web widget config, you can select for the widget to display forms. In the UI config you are only able to display all forms associated with your brand's Help Center. However, you can customize a limited number/selection of forms by adding the snippet for the widget from a different brand.
Say we have 10 forms total. Brand A has 8 forms associated with it. We only want to focus on 3 of them to show up in the Help Center widget, but enabling forms displays all 8 of the brand's forms. I created a Brand B that we don't actually use, associated those 3 forms with it, and used the snippet for the Brand B widget to embed it on Help Center A.
You'd probably want to have a trigger in place to change the brand back to A, and may need assignment triggers updated if you're using brand as a condition, but this allows you to have the subset of forms you're customizing for.