Hi Hitendra,

You can get field permissions and set each permission by setting them to 'true'/'false'.

Adding sample code for setting permissions for each field of opportunity sobject  and you can check for profile by adding below query to list rt query.

AND Parent.ProfileId IN (SELECT Id FROM PermissionSet WHERE PermissionSet.Profile.Name = 'System Administrator').
Hope this ans helps you, if it does select it as best answer.

String parameterValue = ApexPages.currentPage().getParameters().get('Permission_Set_ID'); //Permission_Set_ID reference from URL

}
}
//update field permission for Opportunity  permission
        fieldpermissions fp=new fieldpermissions();
        list<fieldpermissions>rt=[select id FROM fieldpermissions where parentid=:parameterValue AND      SobjectType='Opportunity' ];       
 rt.add(parameterValue );
        
        if(!rt.isempty())
        {
        fp.id=rt[0].id ;
        }else{
          rt.parentid          = parameterValue ;
          rt.SobjectType       ='Opportunity'; 
        }
        
        for(wrapper i:lstwrapperIntString)
        {
        if(i.selectedread ==true){  //vf page if selected read
         rt.PermissionsRead= true;
        }
        if(i.selectedwrite ==true){
         rt.PermissionsEdit=true;
         rt.PermissionsRead= true;
         }
           upsert rt;
        }
           return null;

    }
}