Through Bundle Builder, you can select both optional and required products to add to your bundles:
1.
Go to Bundles.
2.
Select the bundle that you would like to edit.
3.
Select Products.
It is essential that the products you add to your bundle do not use a third-party service to house their variants (e.g. Printful), as Bundle Builder will not function without access to the correct information from Products within your Shopify admin.
Adding Products to Different Bundle Structures
Under Bundles > Setup, you will have chosen to lay your Bundle structure out with either the Single page structure or in Multiple sections.
The process of adding products to your bundle varies according to whether your bundle is on a single page or in multiple sections; follow the correct guide for your bundle structure below.