When creating a custom campaign, how can I manually choose the recipients instead of using any filters?

When you are in the "Filters" section of your custom campaign, click the button at the top of the screen that says, "Skip this step, I will pick recipients manually." 

This will take you to the "Recipients" step where you can select your own list of patients. Type in the patients' names into the "Add More Recipients" section and click on their name to add to the list.