Any photos or videos you take with the Seek Thermal app will automatically be saved to the media gallery within the app which is accessible by tapping the icon located beneath the capture button at lower left corner of the screen, as well as to your device's camera roll.
Android users have the option to delete photos or videos from within the Seek Thermal Media Gallery, which in turn deletes them from your device's camera roll.
iOS users can review and share images from within the Media Gallery, however if you wish to delete content, you must do so from the native iOS camera roll (in the iOS Camera app) or the iOS Photos app.