How do you tag a frame with VLAN header when your device is incapable of VLAN tagging?
You don't. VLAN tags are used on trunk links in order for the devices (usually switches, sometimes routers or servers) on each end to be able to tell which frames belong to which VLANs.
Devices incapable of understanding VLAN tags should be connected to access ports which do not tag frames. The access port itself is configured for a particular VLAN in the switch, but it will not add VLAN tags to the frames exiting the access port.