There is a BLE HID Keyboard code example for PSoC 4. Please check it on PSoC Creator.
The code example sends key presses from a to z and 0 to 9. Optionally you can press a button to activate Caps Lock.
You could modify this code example to send any key press when the button is pushed. Search for a Keyboard HID usage table to see which number maps to what key on a keyboard.