How not to be worried?

Believe in God.

So, how does that help?
If your believe is true, then God’s Will happens:

“If something good is meant to be, God will not withhold it from you; if it’s not, He will make it fail”.

P/S:
What is “good” is judged based on the rewards in the afterlife.
For example, ‘martyred for Christ’ is suffering in the eyes of the world but with respect to the afterlife, it’s a rare Jewel which only a privileged few are allowed (worthy) to endure it .

Hence, don’t worry!
(let it be and in all situations, give thanks!)