I have been struggling on and off with this for the past year... still having completed a few marathons and ultras gritting through the pain (not recommended!). At home, lots of stretching and massaging (ie. foam roller or a large water bottle... or even a small medicine ball if you have access to one at your local gym) cna provide temporary relief. I won't even try to describe these exercise, but if you google IT band foam roller, or something like that, you should get good descriptions/images.
The key is to massage and stretch all the way from the very top of your leg (where the band inserts), all the way down to your knee, not only in the painful area. Stretching all your outer leg muscles (including buttocks), as well as your quads, can provide temporary relief. If you are able to get to a physio, they can help with more intense stretching and massaging (and sometimes even ultrasound or laser therapy in the knee area to help with inflamation in the knee caused by the rubbing of the IT band).
I also use KT/Kinesio tape for races or dureing bad flare-ups; you can google how to apply it for IT band injuries. It may be all in my head, but I swear by it, it relieves much discomfort and prevents pain.
For preventative measures, strengthening the glutes and abductors can often help with alignment, which decreases the rubbing of the IT band on the outside of your knee. But a physio can assess if this is true for you. Sometimes it is due to overtraining....
Also, ice and ibuprofen to reduce swelling in the knee area. Another temporary option.
Hope some of that is useful to your situation!
