What information do you have about Joseph/Josephine Mencl? Bohemia is/was a big place, so it would help to know what village(s) they came from. There are many Bohemian records online, but they involve different archives for different regions of Bohemia, so as a practical matter you need to have some idea of the birth village.
Undoubtedly, there is more than one Joseph Mencl, but I see that there is one already in WikiTree, born ~1827: https://www.wikitree.com/wiki/Mencl-5
Does this profile ring any bells?
You might also get some ideas from looking at profiles of other Mencls already in WikiTree: https://www.wikitree.com/genealogy/MENCL