Dear Sir
In the form 12 a for the month of sep, you should show the no. of employees as of last month, as of august's no. of employees, then in the column of no.of employees left, you should show the no.of employees left and then arrive to the no.of employees in sep.
In the form 10 for sep you should show this employees name, father's name and date of resignation as of the date he resigned on august and the reason for leaving.
Hope you are clear now.
Sindhu