how do I add a possible duplicate
here are the two
L893-5ZD. her parents are Nelson and Cornelia K. and
GZC2-ZPJ. her parents are Narcisse and Melina Roy
both mention Elizabethtown, NY
perhaps the source assignment are root cause of error?
The system usually only suggests a duplicate to be merged when the two profiles are fairly close. These two have different spellings for Elizabeth's surname, different years of birth, and one has parents listed while the other does not.
If you are certain the two Elizabeths are the same person, then you can choose the Merge by ID option in the Tools section.
I have some concerns about the accuracy of the records in GZC2-ZPJ, because they seem to contradict each other in terms of relations and ages, which are different in every record, so I think that there needs to be a closer look there to ensure that they don't all belong to different people. I have not looked as closely at L893-5ZD, but I did find one instance where the ages didn't quite match up, with her supposedly aging 23 years in the 20 years between 1880 and 1900. That alone doesn't always mean that much (lying about ages in the census used to be fairly common) but again, a closer look may be in order.
Regardless, and getting back to the reason I went down that rabbit hole in the first place, both Elisabeth's have 1880 census records, and the two contradict each other on several points. The families are different, the ages are different, and the locations are different. So if nothing else, there are at least two people represented here, and I don't think they should be merged before further research is done.