I honestly don't understand wanting to block a guest who gave a 4* review if they were otherwise good guests and told you that they enjoyed their stay, since Airbnb leads them to think a 4* review is good.
One of my all-time favorite guests, who became a friend and we keep in touch, left me a 5* review. That was because I explained to her how Airbnb punishes hosts for anything less than 4.7 average and that hosts lose their Superhost status for lower than 4.8. When I told her this, she was shocked, asked why Airbnb would basically lie to guests about the ratings, and said she felt terrible because she had left 4* ratings for her previous 2 hosts, when the place was fine and the hosts were really nice, because she assumed a 4* review was fine.
If I got a 4* from great guests who had no complaints, either during their stay, or in their written review, I would just message them to let them know that the 4*s tanked my rating, that Airbnb punishes hosts for that, and if they messaged back saying they had no idea and were sorry, I'd accept a booking from them again and assume they would rate 5*s the next time, now that they were informed.