Preferences - Hotkeys
To open your preferences, click the caret to the right of your avatar on the top of the Tuple contacts directory and select it from the dropdown:
Then select the Hotkeys tab:
Here you can set custom hotkeys to trigger various actions when using Tuple. Just click "Record Shortcut" and enter the sequence you'd like to use for each action.
You can scroll for ever more options than shown in this image.