There are legitimate reasons not to join a physical protest; while it is important to push yourself, marching is not the only way to show up. Get involved with community groups, and ask organizers of events and protests how to help. At rallies (and in everyday life) you can be a witness if a person of color is being harassed—intervening if safe to do so, and seeking help if not. You can offer to accompany someone who feels unsafe. If you sense cause for alarm, use your phone to legally record interactions between police and people of color. Along with public protest, you can help from home by checking in at a demonstration on social media, calling your representatives, writing to local media outlets, and sharing what you learn about racial justice online.
You also shouldn’t assume someone else will do these things. Because there is power in numbers, everyone who steps up brings us closer to a tipping point.