i need to use this app, called hex editor to place a dot in the middle of this dohnut. my teacher failed to show us how to use this app & what to even do. please help and explain !

11. Attached is an image file, in "24-bit bmp" format, of a black donut. Using only a nexeditor, such as HxD https://mh-nexus.de/en/hxd/, put a colored dot in the center of the circle, like this: You may not use any image editing software, only a hex editor. In your submission, state the file offset (number of bytes from the beginning of the file, in hex) of the byte you changed