You can test the frequency response correction I posted
above, entirely for free using software like Equalizer APO, Mathaudio Headphone EQ for foobar2000, or directly in your
browser.
Just copy the text in the Code block, paste it into e.g. Notepad and save it as .txt
With that you can load the preset into your EQ software with a single click.
At the start, I would change filters 1-4 from ON to OFF so that the only correction is the treble region.
Later on you can try setting them back to ON to see if you like the sound better with flat bass instead of shelved bass.