I don't know how to do it through the wizard, I never tried it, usually stay away from them. But a way to do it is creating a table with two fields the name of the table and the next or last key, and of course a function to get the next number from ths table, you can put the function in the stored procedures of the database and set the default value for the field to the name of the function (NextId() for example).

Or you can create an external function and call it after the default procedure for the add button with something like

dodefault() && To do whatever the wizard put in
replace keyfield with NextId() && Filling the key number

Either way this is very common so there's probably a function that does it in the file section