This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
佮 combines 亻 (person) with 合 (fit, join), suggesting a person fitting or joining with others. The exact historical development is uncertain.
A person 亻 beside 合 (fit, join) suggests someone fitting in or joining a group, but the exact meaning is unclear.
For コウ, imagine a person 亻 joining 合 a group and saying 'co-' as in cooperate: co- -> コウ.