I worked at an after-school care program for a couple years when I first moved here. One of our kids consistently struggled with the transition from school to the centre. She'd be snappy and rude and generally hard to deal with.
I don't think it was my idea initially (probably one of my co-workers) but we started talking about a "second day". She'd arrive, all grumpy, and I would offer her the chance to start the day over. She could press the "re-do" button in her mind and a fresh day would be hers.
For whatever reason, it worked.
And maybe it'll work for you. This trick ain't just for kids. Maybe you were late for class, or a co-worker said something that messed you up, or you snapped at your two year old.
And maybe you could use a second day.
How does one get it? It's easy. Just decide to start again. Grab hold of your frustration and let it go. Apologize if you need to, forgive faster than you want to. And then begin again.