Their match was basically set up on Monday Night Raw when Joe attacked Kingston after the champion defeated Sami Zayn and Kevin Owens in consecutive matches.
Here is the updated card:
WWE Universal & Raw Women’s Championship
Seth Rollins and Becky Lynch vs. Baron Corbin and Lacey Evans
Kofi Kingston (Champion) vs. Samoa Joe
The Undertaker and Roman Reigns vs. Shane McMahon and Drew McIntyre
WWE Extreme Rules will take place at the Wells Fargo Center in Philadelphia, PA on July 14.