Reduction In Notice Period

I'm an employee of an organisation having around 4000 employees. Our company does not have CSO. But still it's written in appointment letter of every confirmed employee that he/she should give notice of 3 months before seperation. Kindly guide if we can have support from ID act SO regarding 1 month notice for seperation.

you are not coming under workmen category for whom ID act is applicable. hence either you need to serve three months notice period or else compensate for notice period.

Your question is not clear.
In general, the rule to be followed is standing orders or contract, whichever more beneficial to the employee. Since you do not have certified standing orders, model standing orders will apply. Therefore, if the SO require more than 3 months motice, the it will apply. If not, the 3 months specified in the contract (appointment letter) will apply.
You can not take shelter under ID act to dismiss someone for a lesser period.
Unless, of course there was a misconduct and the termination is based on recommendation of a domestic inquiry and justified by the gravity of the misconduct.