There is no rewind button.
This applies to a lot of areas of life and it is especially true for fat loss.
I frequently hear of guilt and even punishment that people will do to themselves because of some food they ate or what they did over the weekend.
That is no way to live! What's done is done, we learn from it and move on. We cannot go backwards. And for that reason we should not look back except to learn, not to regret.
If you messed up yesterday, last weekend, last month, or even the last 5 years, there is no time travel. So you gained a few pounds, want to know the best way to get rid of it? Stop dwelling on the past, take action today, and don't look back.
"You can't go back and change the beginning, but you can start where you are and change the ending." -C.S. Lewis