I have Apple Watch series 3 42mm

Set your Apple Watch on its charger and make sure that it is charging. ... 

On your iPhone, go to Settings > Bluetooth. ... 

On your iPhone, open the Apple Watch app, then tap the My Watch tab.

Scroll to Music and tap it, then tap Add Music.

Find the music that you want to sync.

garydoan wrote:

I could not

is way to vague

1. what did you attempt?
2. what result did you expect?
3. what result did you receive?
4. in what way did the expectation and the result differ
5. what error messages and the likes did you get provide all intel