Task: Open the Gmail App, Go to the general select the Alternate calendar to Indian Calendar-Hindu(Saka) and theme in light mode. 
Steps:
Open the Gmail App
Click on the Menu Icon 
Click on the Calendar Option 
Click on the More Icon 
Click on the Setting Option 
Click on the General Option 
Click on the Alternate Calendar to make changes 
Select the Indian Calendar-Hindu(Saka)
Click on the Theme Option 
Select the Light Option to change the Theme