This post shows the procedure to un-install MLNX-OS and install ONIE instead.
Connect to the switch via the console port and login to the switch.
This example was taken using SN2700 Spectrum switch.
1. Reboot the MLNX-OS, use the reload command
switch (config) # reload
2. look for the prompt on the console menu and click CTRL-S to enter the Grub menu. Select ONIE
Type YES to uninstall MLNX-OS
Note: This procedure is long and takes 2-3 hours.
Once Completed the system will reboot and ONIE will be loaded.