How do I summon the flower bunnies on Sims 4 Xbox one

You would need to go into the calendar > pick the day you wish to add Bunny day (note you can not add holidays to the current day you are on) > go to add Holiday on the left hand side > Then create the holiday. 

You can create any holiday ad add that you would like to happen 

Bunny day;  add flower bunny 

(Side note I play on PS4 but I dont see why it would be different )