It's over and I need to resign asap: colleague from J2 getting hired at J1

I received 2 corporate announcement emails from both jobs, J1 announcement stating this dude is leaving and, J2 Stating that this new dude is joining. He WILL recognize me when he sees me and his role will work with me right from the get go. I decided that I love J1 and will leave J2 for it lol, how do I quickly resign to my J2 manager? J2 has been fine, slow, chill, I like my manager he's a good guy, but J2 is where my career growth lies. So ANY WAY ---- HOW DO I RESIGN ASAP I literally have no excuse