You may list Your all KVM VM with command:

[root@kvm3 qemu]# virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     vm1.server.tld               shut off

Edit the config file:

[root@kvm3 qemu]# virsh edit vm1.server.tld

Add the following lines to the ‘devices’ part:

<disk type='file' device='cdrom'>
  <driver name='qemu' type='raw'/>
  <source file='/tmp/CentOS-7.0-1406-x86_64-Minimal.iso'/>
  <target dev='hdb' bus='ide'/>
  <readonly/>
  <address type='drive' controller='0' bus='1' unit='0'/>
</disk>

Then find the OS part:

  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
    <boot dev='hd'/>
  </os>

And insert the

    <boot dev='cdrom'/>

to look like

  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
    <boot dev='cdrom'/>
    <boot dev='hd'/>
  </os>

That’s it.
Save the config and boot the VM :)