You can't do anything about it, so just go with it.
If they're religious, you could give them this well-known prayer:
"God, grant me the serenity to accept the things I cannot change,
The courage to change the things I can,
And the wisdom to know the difference."
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.
You can also say, "There's no point crying over spilt milk". That is, the milk is spilt, and you can't do anything about it.
Religious types might say, "Leave it in God's hands" or "It's all part of God's plan".
There's probably lots of other things people say.