Hey

So there are a few exercises that will target this area - but keep in mind that almost all ab exercises incorporate the lower back and strengthen that area as well - so most ab work you do is working that area in conjunction.
If you want to focus on that area I would recommend these exercises
At the gym:
-Machine Back Extension (you start leaned forward and with whatever weight you have chosen, you use your back muscles to push the weight back)
-Back Extension (my favorite!

) It's a static machine that has pads on the top front that you lean against - then you lean forward (rolling your back) and extend your back all the way back and squeeze your lower back - you can also do this with free weights in your hand to make it more difficult.
At home:
- Reverse crunch (laying on your stomach) You extend your arms out in front of you and pull them up off the floor and have your legs straight and lift them up off the ground. (you can modify by lifting just your legs and keeping your arms flat to make it easier)
Hope this helps

and goodluck!