I'm a big fan of London Walks, but there's at least one additional option for travelers who like to see London on foot: The walking-tour company Six in the City--which I had not heard of before today--has created a "Slavery in the City" walking tour for Black History Month. The walk has been very popular and seems likely to be available in the future. The company has some other interesting-sounding options listed on its website. It appears the walks cost £10.
I learned about the Slavery in the City walk from this CNN article: https://www.cnn.com/travel/article/london-slavery-tour/index.html