M.2 Not detected in Bios

Need help with making something else my boot drive. I have SATA hard drive and a M.2 SSD. The m.2 is the boot drive, however after a bios update it put my mobo back on default settings and made my SATA hard drive the boot drive. The bios won’t detect my m.2 to make it the boot drive, however in my files i can clearly see it there with all the files in it. How can i get the bios to detect it so i can make it my boot drive again?