LEDs

Hello friends, I need some help and advice please.

I want a supply of COB leds similar to one I bought in Hong Kong- It's a cluster of 6 leds on a round psb about 38mm in diameter. The KEY thing is that it nbeeds to be powered by a 5v phone charger via a USB cable and none that I can see online allow this. Have to say that I understand little or nothing about resistors and reverse voltage etc and so suggestions and an easy tutorial would be most welcome.

The purpose of these is to illuminate the inside of small shells etc which act as night-lights which I intend to sell to support a charity. I have sourced USB cables with inline torpedo switches but the procurement of the light source is presenting a  problem. I have obtained LED tape which is OK for some appications but want the round (or square- shape isn't important, or size, within reason) COBs for others.

Many thanks in advance,

 Rob