Before searching for a "Cisco ASR 920 IOS download", you must understand one critical fact: The ASR 920 does not run classic Cisco IOS. It runs Cisco IOS-XE, a modern, Linux-based operating system that packages the classic IOS daemon as a single process.

You’re in ROMMON. Recover via XMODEM or USB boot:

rommon 1 > tftpdnld

Or set BOOT=flash:new-image.bin in ROMMON.

You cannot directly downgrade from IOS-XE 17.x to 16.x without clearing config or doing a factory reset (install remove inactive). Be cautious.