Login with ssh to QNAP.

Call virsh.sh with UUID of VM:

/QVS/usr/bin/virsh edit 9a1cafe3-b96e-486b-a461-62a54098734b

Change bootmenu enable parameter to yes:

  <os>
    <type arch='x86_64' machine='pc-i440fx-2.3'>hvm</type>
    <boot dev='network'/>
    <boot dev='hd'/>
    <boot dev='cdrom'/>
    <bootmenu enable='yes'/>
  </os>