Once you have connected your third-party exchange account to the eWallet App, select the main menu point “Exchange”. 

Here you can see the relevant asset pairs, and the amounts that you hold on the third-party exchange.
Note: The amounts are still in the exchange account, only the balance is displayed.
If you want to use ECS in your ewallet - please use the transfer function , to load ECS from your exchange account to the eWallet app.