If someone tells you to let sleeping dogs lie, they are warning you not to disturb or interfere with a situation, because you are likely to cause trouble and problems.

For example:

I thought about bringing up my concerns, but decided instead to let sleeping dogs lie.

I was tempted to ask my boss why she was upset, but I decided to let sleeping dogs lie and not bring it up.

He knows about the mistake, but he hasn’t said anything, so I’m just going to let sleeping dogs lie.

While I want to address the issue, I also realize that it might cause more conflict, so I’ll let sleeping dogs lie for now.

Tradução:

A expressão em inglês “let sleeping dogs lie” significa deixe as coisas como estão, não mexa no que está quieto, não procure sarna para se coçar.