Footstep sounds are near the 6k range, so all you have to do is boost that frequency. The lower frequencies are usually explosion noises, so lower those. If you have a equalizer then gradually increase the freqs near 6k and lower the low freqs
Here?s how to do it with the built in Windows equalizer
Right click the bottom right speaker and go to ?Playback devices?
Right click your headphones and select properties
Enable the Equalizer under Enhancements and click the ??? near the bottom left
Set your Graphic EQ like this
Remember to turn it off after you?re done playing siege by checking the ?disable all sound enhancements?