You'll disembark and follow the ICQ signs.. clear passport control... and enter the domestic terminal.

The TG domestic lounge is certainly fine by US standards but much more limited than the TG international lounges which have quite nice food and dessert selections.

While waiting for your international return flight (assuming you're returning on Thai) you can use the spa for a 30 minute massage (longer and more extensive treatment options for F).

But the domestic lounge does not offer massages.