hem, plait, braid, queue
緶 centers on textile work that involves folding, twisting, or interweaving material: hemming, plaiting, braiding, or forming a queue (a braid of hair).
緶 combines 糸 (thread) with 便, which likely contributes the sound and may relate to the idea of arranging or making convenient, but the exact historical development is uncertain.
The left side is thread 糸, and the right side 便 looks like a person arranging something. Picture using thread to hem fabric, plait strands, or braid a queue of hair.
For ヘン, imagine a hen pecking at a braided hem: hen -> ヘン, and the thread 糸 is woven into a neat braid.