Theres no easier way other than finding the manga and trying to put it in that list, it'll tell you if its already in the list
only thing i can think of checking in your browser history depending on if u delete your data or not.
otherwise a tip for future reference use notepad if your on windows and have a summary eg and if ur on mobile use Samsung notes or if your on iPhone there's probably an app and on notepad/ Samsung notes there's a feature ctrl f or and u can search for the manga/manhwa or whatever ur looking for (on Samsung u can use the similar feature as ctrl f ijdk how to do it cause i haven't done it in ages)
windbreaker *Read to ch40* last read 01/01/2000 and last read if u want to know when u last read it
example is at the bottom cause i moved the text around
How do I check if a manga is already in my list? Other than readding it getting the pop-up since most of my lists are already full and the pop-up will just say that.