You can place an order in 2 ways as below:
Go to Detailed Quotes page, tap "Paper Trading" on the bottom left, choose a Paper Trading Account to submit an order.
Go to Detailed Quotes page, tap "More" on the bottom right, then tap "Papertrade", choose a Paper Trading Account to submit an order.
Tap "Discover" - "Paper Trading", choose a Paper Trading Account, then tap "Trade" to submit an order.