How do you tune a headset?

assuming you mean via software, there are multiple programs to do so. on Windows, there is a high chance there is a default tuner app(dolby, hp's inbuilt tuning app etc.). for Android, there is an app called wavelet which gets the job done well. now on how to set the values. the sliders correspond to the prominence of various frequency ranges. if your headphones dont play bass too well, fiddle around with the left-most sliders, if treble is the problem, fidget with the right most ones and for mids, the middle few would do the trick. there is no right tuning per se, do whatever feels right to you and what makes the type of audio you listen to sound the best.