Lets all not mention that the pill is hollow, so any attempt to drive this at a higher output with another driver/LED is a complete waste of time. Some of those have a solid pill and can be modded, but this one would cook the LED fairly quickly. If you were to just swap the LED and use the driver, it’s fine, but don’t even bother changing the driver. Throw it in the bin or gift it as is.

Remove the tailcap, get your DMM and set it to measure amps, place the negative lead (-) onto the battery and the positive (+) onto the threads or edge of the battery tube. This is the way most measure the driver current.