go back on something—fail to fulfill a promise, agreement, etc.:
- You should never go back on your promise to a child.
go back to something—
1. return to smth. as in conversation:
- Let’s go back to what the chairman was saying.
2. bring smth. back to the mind:
- Whenever grandmother talks, she always likes to go back to her younger days.
3. have a history extending backwards in time:
- Phrase as black as a coal, with its variants, goes back to Old English times.