Hi Sachin,
You can archieve focusing to the next element with the following steps:
1) On your first Textbox, enter it's properties and go to Events. Set the On Enter key press event to Nanoflow and create a new Nanoflow:
2) On the created Nanoflow, simply use the Activity Focus next
If you don't have such Activity, download the following Marketplace module:
This way, when you press Enter, you will be focused to the next element:
I hope that solves your question, best regards!