Way 1 · best default
It's going to be OK
Simple comfort. You're telling them this bad moment will pass.
Examples
Hey, it's going to be OK. We'll find your passport.
It's going to be OK, the doctor said it's nothing serious.
In a conversation
A: I've missed the last train and my phone's nearly dead.
B: It's going to be OK. You can stay at mine tonight.