en_tn/jon/03/10.md

God saw what they did

"God understood that they that they stopped doing evil actions"

God changed his mind about the punishment which he had said he would do to them

"God changed his thinking about the punishment that he had said he would do to them" or "God decided not to punish them as he had said he would"

and he did not do it

This can be translated more specifically: "and he did not punish them" or "and he did not destroy them."