Access 2013 - Sample DAO code

My OS is win 7 prof 64 bit and i use Access 2013.  i have a small password creating App which works fine without problems.  I now want now to check the created password with those that have been created before, and if a duplicate exists, then to re-generate the password code again, if not, then to append the password to a field in the table.
The name of the table, is tblMainpassword.  The name of field where the old passwords are : strcreatedpwds; and the name of the variable holding the newly created password is : strgeneratedpwd.

Hope the Experts can give me the sample syntax on how to go thru the field in he table one by one to check if it exists or not.  
Thank u.