How do you determine a fake thumb drive's true capacity and change it to that?

Got one of those Chinese counterfeit USB flash drives. It says it's 128 GB but I know for a fact that it's nowhere near that.

In Windows there are several softwares which help you determine if the capacity the drive is communicating to the computer is true or not. They do that by writing and reading files onto it. A famous software for that is H2testw.

Is there a similar method in Linux? Or any method that would tell me the true capacity of the flash driver?

And after finding out what the true capacity is, how can I change (flash?) the drive to that capacity?

Thanks! ?