You shouldn’t have to, it subscribes to the top grid and when you change the top grid it automatically re-runs the query. However if you want to force it to refresh (IE you add more data somewhere else) you can do this
//Add this using at the top of your class
using System.Reflection;
//On "Refresh" or button click
MethodInfo mi = bdvLeaveUsage.GetType().GetMethod("invokeExecute", BindingFlags.Instance | BindingFlags.NonPublic);
mi.Invoke(bdvLeaveUsage, new object[]{ true });