How to modify a ContorlTemplate by code?

Dear all:

I have a contorl with a ContorlTemplate by follow:

<ControlTemplate x:Key="MyControlTemplate" TargetType="{x:Type
local:MyControlTemplate}">
<TextBlock x:Name="TB" Text="1111"/>
</ContorlTemplate>

If I want to dynamic change the Text of the TextBlock By code, how to
do it?

Suppose I have got the ControlTemplate CT.
How to find the TextBlock in CT?

thx a lot.