The children of Israel were faced with the killer Goliath. They kept running into hiding whenever he appeared. He was too big for them, they had no strength to match his own, they were faint hearted and scared to their bones.
But there was one who remembered the power and faithfulness of God. How He helped him to kill a lion and a bear, he knew that the same God could help him conquer this giant of a man, and God did show forth, like with the lion and the bear, God helped him kill Goliath too.
Has God ever granted you any victory in the past? Has He answered any of your prayers? Has He ever delivered you? Remember those times and refuse fear, He will deliver you from this present trouble too, like He did in the past.
Then I said to you, Dread not, neither be afraid of them. The Lord your God Who goes before you, He will fight for you just as He did for you in Egypt before your eyes. (Deuteronomy 1:29, 30 AMP)