Cmos Setup

I ahve this old 486 Osborne Computer , running Windows ’95 16 Mb ram Phoenix bios I am in the process of fitting a cd-rom into it and i need to get into the Cmos to enable the Primary and secondary HDD , can any one tell me what is the Key or Keys to entrer the Cmos in this system , i have tried everything i can think of ,includung treating it like a Compaq and unpluging the Mouse , but with out success, i ahve limited time to do this so i need know URGENTLY please
Thank you in advanced.