If you’re not a native speaker of English, you might struggle to hear and to reproduce the difference between d and th (ð) sounds. Don’t give up! If you sing ‘dey‘ instead of ‘they‘ or sing ‘dose‘ instead of ‘those,’ you sound as if you have a very bad cold. To a native speaker, you sound as if your nose is blocked. That’s not an attractive thought to put in their mind. You can’t avoid the soft th of English. The word the is the most common word in the English language.
Listen to the Mamas and the Papas singing California Dreaming. Focus on the clear, clean d of dreaming, day and down. Fix that sound in your head. Enjoy the bathtub dancers.