While in the 1SE camera, press and hold the record button at the bottom of the screen. Release once you captured the second you'd like to use. This will record a video and automatically grab the last second of the video. Quick and easy!
You can even launch directly to the app's camera from our notifications if you enable this setting!
FYI: The second will be applied to the day you selected and the whole video will be saved to your camera roll. Access the whole video in your Photos app if you'd like.