Since Trump did this. Biden should counter by having a rally in say West Virginia or North Dakota.
Trump going to south Bronx is him riding on the narrative that he is making inroads with AAs and Hispanics as what polling and the MSM media suggests. Biden going to West Virginia would be nonsensical as there are no talks about him making inroads with rural whites nor the polls are showing so, no evidence to suggest that currently.
It still makes no sense to go to an area you aren't going to win in a state you aren't going to win. Trump lost the Black vote in his own primary to Haley if precinct analysis is accurate so polling is not to believed.
Trump won the Black vote by about the same proportion he won the primary as a whole. If you look at precinct maps of cities in competitive primaries, Haley usually won the White yuppie areas but Trump won the Black areas, often by 50+%. These precincts had very few votes however.