I used a new cast iron skillet to cook bacon. can i use the remaining fat to season? if yes, how?

Any fat or vegetable oil is fine, be sure to over heat the skillet, then let it cool. Repeat if you choose, but when it comes to iron you will have as many suggestions as you have suggesters about how to season. I use peanut oil, but more important is the ongoing seasoning. NEVER use any type of detergent to clean your pan or pot. After each use clean with hot water, then wipe dry. I clean and dry while the pan is still hot from cooking. This seems to work well retaining and improving the "season" of your utensils. I have treated my iron pots and pans this way for many years....they are excellent no stick, even heating tools. They will get better after each use, until a family member cleans one with a detergent. Then you just start over!

The problem with bacon is that it's cured with sugar and nitrates unless you cured your own using raw pork belly. Sugar baked into cast iron is sticky. There are so many pure fats to season with. I use beef tallow, lard (good stuff from pastured pigs), rendered chicken or duck fat or grapeseed (least favorite) oil.

Just rub it on and put in a high heat oven upside down with a drip pan underneath. 350-400 for an hour. Some people don't like using bacon for various reasons but it was the traditional seasoning for cast iron.
Just make very thin coats for the seasoning process to avoid drips.