In old documents, 手柔らかに is sometimes written, but in modern times お手柔らかに is common.
gently; mildly; leniently · go easy on me/us/them; don't be too hard on me
The exact derivation is uncertain; the spelling 手柔らか combines 手 (hand) and 柔らか (soft, gentle), suggesting a gentle hand or mild manner.