I can pronounce th sound θ but the other th sound ð, I can't. I mean the th sound in which there is a vibration in throat, I try to pronounce but there is just no vibration when I pronounce. How to do that?

When I pronounce th there is only voiceless sound. I am struggling to pronounce voiced th sound but I don't know how.

https://pronuncian.com/pronounce-th-sounds Here it says vibrate your vocal cords but how?