If someone slaps you on the right cheek, what did Jesus say to do?

Answer: Turn the other cheek too

Instead of "eye for eye," Jesus taught not to resist an evil person but to turn the other cheek as well.

“You have heard that it was said, ‘Eye for eye and tooth for tooth.’ But I tell you not to resist an evil person. If someone slaps you on your right cheek, turn to him the other also;”— Matthew 5:38-39 (BSB)