I’ve done a blog post a while back about how to set up IFTTT to work with OpenGarage:
“Alexa, Open Sprinkler Zone 1” — How to Use IFTTT with OpenSprinkler (and OpenGarage)
admittedly since IFTTT has changed quite a bit some of the snapshots are not the same any more. I will try to update it soon. I believe the setup is still similar.