A common response to a smoking relapse is to feel that you have failed. If you've returned to regular smoking, don't be too hard on yourself. Find out where you went wrong and think of strategies for next time. The more you learn about the quit smoking process, the more you understand that the number of attempts you make is an important factor.
If you are ready to try again, you can read more about the ways to quit smoking and getting restarted on your quit journey here or read more about relapses.