This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
揳 combines 扌 (hand) with 契, which likely contributes sound. The exact historical development is uncertain.
The hand radical 扌 beside 契 suggests an action, but the specific meaning is unclear. Imagine a hand performing an unknown task with a tool shaped like 契.
For セツ, picture a hand setting a tool: set -> セツ, even though the kanji's meaning is uncertain.