How to make changes in army documents?

Are you working in Army as now? If you are working as on now you can get the name changed as follows.
You have to fill DA Form 4187 and submit the same to your commanding officer.
Along with the above application you have to submit proof of your name change.
As mentioned by you, you have already obtained the Gazzette publication. A copy of that gazette can be attached to your application as proof of your name change.
Once you submit the same, the concerned officer will approve the name change and your documents will be changed accordingly.

If you are not in the service as on date, the changed name will not be reflected in your army certificates. They consider the records of the discharged person as historical documents. In those documents, your name as in the records at that time only will continue.

But you can apply and get a certificate from the National Personnel Records Center showing your current name and as it was in the certificates during your service. They will clearly mention the name when you are in service and the name after the change. You can get this certificate and this will be useful to show your name change.

You have mentioned that there is some mistake in the name in the property documents. It means when you bought this property or made it in your name at that time some mistake has cropped in there. In such cases a correction deed is to be again signed between the two parties that is yourself and the party from which you have bought this property. There is a standard procedure for that and a correction deed comprising of earlier facts about the property in brief and then the mention of the correction itself in the name or whatever data is there is to be carried out. It is done in the same registrar's office where the original property deed was signed between the two parties.

Army administrative office can not change that name at their level. Once the deed is rectified then you can give a copy to them so that they can also correct the same in their records.

One thing which I will suggest you to check at your end is that there should be a consistency of name in all the records like educational certificates and PAN card and Aadhaar card and property document. Wherever there is mismatch one must go for the individual process for it. Correct name in one document does not entitle us to make a correction in some other document where mistake is there. The name in your Gazette notification is only a proof of your correct name but the procedure to change name in property document is required to be done through the rectification deed only.

Since it is related to property document and while making this document, as per your statement some mistake has cropped in with respect to your name. This needs to be corrected at the earliest so that it is free from mistakes in your property document. In your case, correction deed has to be made between you and the party from whom the purchase has been settled. Such a documentation hereinafter would be known as correction deed which would provide the nature of correction of any nature( in your case, it would be the correction of your name). There will be incorporation of details of the property. There would be the inclusion of the names of both of you ie buyer and seller with the proper initials and the same is to be signed by the authority of the Registrar - office.
Once this is done, you may hand over to military authorities for the further initiative to be taken up by them.