This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
擑 combines 扌 (hand) with 戢, but the historical development and original meaning are uncertain. The exact role of 戢 is unclear.
The hand radical 扌 beside 戢 suggests an action, but the specific meaning is obscure. Imagine a hand performing an unknown task with a complex tool.
For セツ, imagine a hand setting a complex device: sets -> セツ, though the kanji's meaning remains uncertain.