I hit my eyebrow a week ago and it is still swollen. How can I reduce this swelling?

Gentle ice compress. Ice compresses may help. Manual lymphatic drainage may help. Gentle pressure may help. However if you have a hematoma, aspiration may be advised.
Ice, arnica. Ice applied 20 minutes at a time helps. Arnica and bromelian are homeopathic medications that help with swelling and bruising.
Time. It will take time. If it feels like there is fluid under it then see a doctor for possible needle drainage.