Attachments would not be able to be passed along using app links/custom URL scheme. In Survey123 attachments can only be taken using the devices camera, uploaded from the devices file system, or set as default using an image in the surveys media folder.
If you are editing existing features I would suggest using the Survey123 Inbox. We have some enhancements regarding editing existing images in the Inbox, and have some of this functionally partially implemented in our current Beta builds available in the Early Adopter Community.
Please use this EAC documentation link for more information on viewing and adding image attachments for existing features in the inbox.