In the first part. How did Sinbad’s fortune change for the better?

Sinbad had inherited much wealth from his parents, but he spent it quickly due to poor, youthful decisions. Without any money, he set off to sea as a merchant sailor. He quickly grew accustomed to the sea, and began to make money at various ports.

One day, the ship docked on an island, and the sailors made a fire, only to discover that they were actually on the back of a whale. As the fire started burning, the whale dove deep into the ocean, leaving Sinbad floundering on a piece of wood as his ship fled without him. He was stranded in the middle of the sea.

Eventually, he drifted onto an island. There, he helped a horsegroom to save a mare from being drowned by a mystical, powerful sea horse. He then learned that the horsegroom served King Mihrage, who ruled the island. The horsegroom gladly brought the sailor to meet Mihrage.

The king graciously received Sinbad, giving him everything he needed. Sinbad befriended other merchants and sailors on the island, so he was in a position to recognize a chest with his name on it when a ship docked on the island one day. He quickly realized that this was the very ship that had left him. Sinbad's captain initially doubted the sailor's claim - they all believed Sinbad had drowned - but was eventually convinced.

Before leaving the island, Sinbad gave King Mihrage some of his rediscovered belongings as gifts, and the king bestowed him with valuable gifts in return. During the ship's return to Baghdad, Sinbad progressively traded these gifts for items of more value, so that he was incredibly wealthy when he arrived home.