How do i configure GRUB to triple boot?

I have a laptop with windows 8 pre installed. I installed on that laptop RemixOS using the guide here.
And after a while i decided to install ubuntu 17.04, so I resized the windows 8 partition to create a new partition of 50G for ubuntu. After that I installed ubuntu 17.04 using a live USB but when I turn on my laptop it only shows RemixOS and Windows on the boot menu. How can i configure or fix the boot menu to also show ubuntu?