A double-chin is a collection of fat, so in order to get rid of it, you need to reduce the amount of fat.
Now, there is no way to target where you want to burn fat. You burn it all over your body, or nowhere at all.
Thus, the best way to get rid of double-chins, is to take a look at your diet, which is the number one way to reduce fat naturally.
If, after losing a lot of fat, you still have a semblance of double chins, it could be residual skin, which is something that is most commonly fixed with minor, non-invasive surgery.
As for the exercises you mention, I have tried to find some sources for it, but all I can find are some articles here and there, written purely for clicks.
Some of them involve slapping your chin, pinching your chin, and doing a bunch of - let's be honest here - stupid stuff.
Notably, none of them source any actual research, so as far as we know, some dimwits are actually writing these articles for clicks and ad-revenue.
So no, all evidence suggests that this is all bullshit.
Bottom line: If you have too much fat, you should adjust your diet.