In the Text Entry Box field, I want to restrict the user to type SD1234 text. Where first two characters should be "SD" and rest can be any numeric values. Please suggest if I can achieve this validation through IF condition of the advanced action.
This is possible with the TEB Validator widget.
Here's a live demo displaying your specific use case:
Here's a link to the Cp 5.5 project:
Here's more info about the widget:
Let me know if you have further questions.