having trouble cascading two rainbowduino to work

Hello!

I am new here. I just got two rainbowduino boards and I am trying to connect them to work so that the two LED matrix can serve as one screen. I do not have an arduino board to be the master, so I connect my board to my laptop to upload my code directly.

However, it seems simply connect the two boards together won't work. I have searched the Internet, it looks like I need to assign different addresses to these two boards but I do not know how, so can any knowledgeable people help me solve the problem?