I would say what Divine said but don't call it a mistake. Just say you tried a tactic to improve the ranking, it didn't achieve the result you wanted, so you want to go back to the old terms and maybe try something different at a future date to see if you can move it even higher. Frame it as a strategy, not as a mistake. Even say, "I am attempting to figure out what our competitor is doing and beat them at it to get a higher ranking, so it's a little bit of testing what works."

I mean, to me it doesn't even sound like you made a mistake. A mistake is like an error. You didn't make an error. You tried a tactic, it didn't work, so you are going to try something else. It sounds like it's a continuously moving target anyhow, so it's okay to make changes again....

Seesaw