This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
扜 combines 扌 (hand) with 于, but the historical origin and meaning are uncertain. It may be a phono-semantic compound, but the exact development is unclear.
With no clear meaning, focus on the shape: a hand 扌 beside 于. Imagine a hand holding an obscure tool shaped like 于, but its purpose is forgotten.
For ウ, picture a hand (扌) making a 'u' shape while holding the 于 tool: 'u' -> ウ.