Could you provide us a bit more detail please?
In general, once you give Spinoff access to your Photos library, the app will have access to your images. As you may know, you can check the access setting through [Settings app > Privacy & Security > Photos > Spinoff].
In the editor, when you tap on the [+ > Background > Image > +Import > From camera roll], you should see the photos in your Photos library. You can also select a specific album by tapping on the album title between the 'Cancel' button and the 'Done' button on the top.
If it does not work as above, or your need is different, please do let us know. Thank you!