What is a synonym for let by gone be by gone?

Excuse me, I came across the phrase "let by gone be by gone" and I'm having a bit of trouble understanding its meaning and finding a suitable synonym. Could you possibly assist me in identifying a term or phrase that captures the essence of this expression? It seems to suggest moving on from past events and not dwelling on them, but I'm curious if there's a more concise or commonly used way to express this sentiment.