The Farewell of Canglan
From loveless translations:
After a great battle, the weakened demon tribe resurrected the ancient demon lord Dongfang Qingcang, whom they thought would lead the demon tribe to victory over the heavenly realm. Unfortunately, the mighty demon lord accidentally swapped bodies with an inexperienced flower-spirit. What should've been an epic war of destruction between the three realms became a slapstick romantic comedy that will create an uproar in the realms instead.