How to insert the field value in infopath form?

I have an infopath form ,i am able to retrieve the value from the field using:

MainDataSource.CreateNavigator().SelectSingleNode("/my:myFields/my:fie开发者_运维技巧ld1", NamespaceManager).Value;

But my question is, how can we insert new value in to that field?

Please go through all the properties,You can find

MainDataSource.CreateNavigator().SelectSingleNode(
    "/my:myFields/my:field1",NamespaceManager).SetValue("Required value");

I hope it helps