Boot Option to switch from UEFI to legacy Bios is disabled

 If you see the boot options under the VMware VM that already enabled and want to switch legacy follow the below steps.

Note:The process to make the VM bootable again after changing the firmware is quite a pain.You need to create a new boot partition on an MBR-partitioned disk.Then you need to boot from a Windows-installer ISO and run a bunch of commands to create a new BCDstore, add a new boot-option and stuff like that.

From vCenter Webclient:

    Power Off the VM

    Edit VM settings ->VM Option->Boot Options

Firmware Boot option is EFI and disabled.

    Disable Virtualization based security and now you can change Firmware to Legacy BIOS.

    Now Power ON VM