Welcome Anusha.
You can experiment with Pitch, it sets the speech pitch for the TextToSpeech.
The values should be between 0 and 2 where lower values lower the tone of synthesized voice and greater values raise it. The default value is 1.0 for normal pitch. Changing pitch can make an installed voice seem more masculine or feminine sounding. Otherwise, follow Tim's advice.
What you can do with the Blocks is described TextToSpeech
also see Setting text to speech to an English accent and How do I change voice with Text to Speech?