Can probably just get a USB battery eliminator.

https://www.amazon.com/T-HOT-Battery-Eliminator-Supply-Adapter/dp/B0891YF3FJ/

Want to make sure you get the right one for the number of batteries it uses. Like assuming the thing uses 3 AAA batteries in series which is pretty common for LED stuff you want the 3aaa version.

The little USB plug should have a built in voltage regulator that sets the voltage to what's expected of all the batteries and the spare cell looking things are just jumpers to take up space and connect across where the batteries would normally be.