You have three options when it comes to adding bacon to ground beef.
Grind the bacon and mix with the ground beef before cooking/making patties.
Add cooked bacon to your ground beef.
Use the bacon fat/drippings to cook the ground beef.
Warning: adding bacon in this way requires you to cook the meat ALL the way through. Food poisoning is a real thing and even more important when it comes to dealing with pork products.
Another open is to cook the bacon BEFORE grinding it and adding it to the ground beef. Cooking the bacon first still allows you to have your burgers rare to medium-rare without having to worry about any foodborne illnesses.
You can also add bacon fat to lean ground beef. Once you've calculated how much fat is required (see matrix), add the bacon fat to the lean ground beef before cooking.