This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
趈 is a rare character composed of 走 (run) and 占 (occupy/divine). The exact historical development and original meaning are uncertain.
Since the meaning is unclear, focus on the shape: 走 (run) enclosing 占 (fortune-telling). Imagine running to a fortune-teller, but the outcome is unknown.
For タン, picture a tan-colored running track (走) with a fortune-teller's booth (占) at the end: tan -> タン.