usually, in ROMMON you would use the boot command followed by the name of the IOS file you want to boot. Be aware though that there is a different way to boot the system in IOS version 12.2 (not sure if that is what you have):
Boot Changes in Cisco IOS Release 12.2
Cisco IOS Release 12.2 changed the behavior of the ROM monitor (ROMmon) during the bootup sequence. Previously, users could issue the break signal during the bootup sequence to break into ROMmon, and then immediately boot a new Cisco IOS image using the boot command.
This behavior is no longer allowed when the router is using a boot image that is based on Cisco IOS Release 12.2, because interrupting the boot process could leave the hardware and software registers in an unknown state. Instead, use the following procedure when using a router with a Cisco IOS Release 12.2 boot image:
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...