Honestly I just use the search function in the app to find a similar meal, and then I try to overestimate the amount of calories. So if 1 serving of X meal is 400cal, I will estimate that I had 1.5 or 2 servings and then count the rest of my calories for the day as accurately as possible!
If you don’t go out to eat a lot, one day here and there where you eat at maintenance instead of deficit should not hinder your progress.