This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 畃 is uncertain. It visually combines 申 and 勺, but the original component relationship is unclear.
With no clear meaning, picture the left side 申 as a person speaking and the right side 勺 as a ladle. Perhaps it once meant giving orders or ladling out instructions, but treat this as a mnemonic only.
For シュン, imagine a person named Shun using a ladle to serve soup while speaking: Shun -> シュン.