If you already have a logo image placed on your broadcast, to enter the edit mode, you’ll need to tap

button again. Then, image settings buttons will appear around it.
To reselect a new image, you will need to enter edit mode to delete the current image first, then tap

button again, so that you can choose a new image from your photo gallery. Once done selection, tap on

button. Then you can find the new logo image or sticker on your broadcast.