Which flintstones episode did they take a trip to the desert and betty and Wilma were turned into harem girls and Fred and barney had to dress like harem girls to try and save them?

The episode you're referring to is titled "The Hatrocks and the Gruesomes," which is the 28th episode of The Flintstones. In this episode, Fred and Barney travel to a desert where they encounter the Gruesomes, who capture Wilma and Betty, turning them into harem girls. To rescue them, Fred and Barney disguise themselves as harem girls. The episode features classic Flintstones humor and adventures.