Hi Shatrughna,

Use the below code it may helpful for you.

public class  RequestBodyApex{

    public class WrapperClass {
        public Platform platform;
    }

    public class Platform {
        public Record record;
    }
    public class Record {
        public Query_type query_type;
        public String consumer_title;
        public String consumer_first_name;
        public String consumer_surname;
        public String consumer_date_of_birth;
        public String address_line1;
        public String address_line2;
        public String address_line3;
        public String town;
        public String postcode_2099407766;
        public String ERP_Set_Status;
        public String Customer_status;
    }
    public class Query_type {
        public String content;
    }

    public static void requestBodyMethod(){
        String requestbody = '{"platform": {"record": {"query_type": { "content": "11"},"consumer_title": "Mr.","consumer_first_name": "Shatrughna","consumer_surname": "Salunke","consumer_date_of_birth": "1971-10-08","address_line1": "19","address_line2": "","address_line3": "","town": "Pune Hinjawadi","postcode_2099407766": ""}}}';

        WrapperClass requestbodyObj = (WrapperClass) JSON.deserialize(requestbody, WrapperClass.class);

        if(requestbodyObj.platform != null && requestbodyObj.platform.record != null){
            requestbodyObj.platform.record.ERP_Set_Status = 'XXXXXXXXX';
            requestbodyObj.platform.record.Customer_status = 'AAAAAAAAAA';
            requestbody = Json.serialize(requestbodyObj);
        }
        
    }
}

I hope you find the above solution helpful. If it does, please mark it as Best Answer to help others too.

Thanks and Regards,
Sachin Arora
www.sachinsf.com