As i got this for free from Cisco and i had to get rid of the firmware and license, OpenWRT is what we actually need.
Step1. Open the case.
Step2. You need a UART serial console. For this i used Raspberry Pi 4. Pins and how to can be found online, just google it.
Step3. Once you are connected, you need pre-flash using UART serial.
Step4. After pre-flashing is done, AP is listening for a 192.168.1.1 TFTP device from where to download rest of the firmware.
Step5. I used TFTPD32 for this, very easy to send the firmware. Just to make sure your server is configured to 192.168.1.1