play along with (someone)

Translations
подыгрывать (кому-то)
She decided to play along with his joke to keep the mood light.
Она решила подыграть его шутке, чтобы сохранить лёгкую атмосферу.
Definitions
To pretend to cooperate or agree with someone, often in order to avoid conflict or to achieve a particular goal, even if you do not truly agree or support what they are doing.