Try one of the 40 minute HIIT and abs workout from the programme.
When you join the programme I do an initial benchmark test to see what level you are at, and I programme the videos that are right for your current fitness and any injuries or issues you may have.
Strengthen your lower abs with these exercises. This video is 10 minutes long, so if you are trying this for the first time I suggest you do the first set of exercises (5 minutes) and try to build up to the second set and do the full 10 minutes.
Do this workout regularly to improve your core strength. This ab workout is just five minutes, but it is intense so be sure you perform the exercises safely.
This is workout is suited to intermediate level, not for beginners.