The general dearomatization method works as follows:
Locate the aromatic electron fog.
Locate special bonds, that should be single ( e.g. all the bonds around a trivalent nitrogen should be single).
Place alternating single and double bonds instead of aromatic ones.
This method does not check by default if Hückel's rule is valid. Molconvert has options, that check the validity of Hückel's rule:
"huckel": checks the validity of Hückel's rule, if not valid dearomatization isn't carried out, but no error message is sent.
"huckel_ex": if Hückel's rule is not valid, the program terminates with an error message.