What are you trying to do that you can't?
Adding the custom how-to's shared in galleries to the galleries page is a data mismatch: the galleries page has galleries, not how-to's. How-to's are supposed to be in the guide.
What is your idea?
Organize the how-to section of the guide to make a place for gallery shared how-to's, in addition to other how-to's.
What are you trying to do that you can't?
Adding the custom how-to's shared in galleries to the galleries page is a data mismatch: the galleries page has galleries, not how-to's. How-to's are supposed to be in the guide.
What is your idea?
Organize the how-to section of the guide to make a place for gallery shared how-to's, in addition to other how-to's.