If that doesn't work (rare, but who knows)...
Both hot and cold have their applications, but...
With a seized atty that's been in use, 20 minutes in the freeze can make the difference.
With a new one, other than machine oil on the metals, the O-Rings are usually pretty dry.
I'd start with a hot bath, and dish soap to get things lubed.
At least it's an RDA... no glass to worry about gripping too hard.
Rubber bands, silicone jar lid opener sheets, and latex gloves are handy too (no pun etc.).
