Once you have connected your third-party exchange account to the eCredits Wallet 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 eCredits Wallet App - please use the transfer function, to load ECS from your exchange account to the eCredits Wallet app.