① Go to the top-level power-up rem named Custom Icon via Ctrl(⌘) + P command
② Save your Icon image there neatly ('square-shaped' images are preferrable for lining up)
③ Just copy a 'square-shaped' image as a reference, and then paste it to in front of a rem. That's it!
Need-to-Know
Before uploading images to the RemNote AWS S3 server, Lowering(Compressing) image size would be preferrable for page rendering speed and optimize your local backup size and storage consumption.