I mostly use Beyond these days, so I don't have page #'s but in chapter 4 just before the Acolyte entry it has this:
quote:
Customizing a Background
You might want to tweak some of the features of a background so it better fits your character or the campaign setting. To customize a background, you can replace one feature with any other one, choose any two skills, and choose a total of two tool proficiencies or languages from the sample backgrounds. You can either use the equipment package from your background or spend coin on gear as described in chapter 5. (If you spend coin, you can’t also take the equipment package suggested for your class.) Finally, choose two personality traits, one ideal, one bond, and one flaw. If you can’t find a feature that matches your desired background, work with your DM to create one.
So basically you take a standard background feature/equipment and then customize the skills/tools/languages/personality traits. Or you work with DM to create a custom feature, but I never really find that part necessary personally. One of the published ones almost always works for me, maybe with a skill or tool swap here or there.