Hello, my name is ***** ***** I'll assist you. I'm sorry you're having trouble with it.
Please check attached image file taken from related manual and select M3 or S option in changing picture size option to get approx 300dpi, you may need to process the picture in a photo editing software to set exact 300dpi resolution.
I trust my input will help you out. Please feel free to respond if you have any additional questions.