Hi!
You can use play_tween() to get the tween to play.
Using restart_tween() will play the tween again, from the original position.
You've also got:
pause_tween(): Self-explanatory. Use play_tween() to get it running again.
stop_tween(): Stopping the tween will stop the tween AND "kill" it. You will need to load_tween() again. However, if you got the "Persist Tween Information" on, you're tween won't be killed, and using play_tween() will start the animation from where you are.
If you head to the github and download the project, you can take a look at some of the examples I'm working on.
Hope it helps, but let me know if you need to chat!