To add (using iOS):
Go to Quotes.
Tap on the search bar to open the list of all the groups of instruments available for trading.
Tap the + icon beside the instrument you want to add and it will be added to your Quotes list.
To add (using Android):
Go to Quotes.
Tap the + icon, and then locate the instrument from the groups presented.
Tap on any instruments you want to add, and they will be added to the list presented in Quotes.