Buy multiple litter trays and in multiple locations over the house or area bunny is choosing to make as a toilet.
Get the right litter
USE:
* Newspaper
* Wood stove pellets (these are used as fuel for woodstoves, but are actually great as bunny litter pellets.)
Do NOT Use:
* No clay litter! This can cause serious respiratory problems.
* No Cat Works litter! This can cause zinc poisoning and death.
* No Pine or Cedar litters! These can also kill your rabbit.
1) Line the bottom of the tray with a few sheets of newspaper
2) add the eco wood pellets on top
3) Add two/three sheets of newspaper on top of pellets
4) Add hay on top
Rabbits eat where they poop, so adding hay into the litter boxes aids litter training. Also remember to change litter boxes once a day and provide fresh hay morning and night.
http://www.rabbithaven.org/litter-training/
https://bunnyapproved.com/litter-box-set-up-for-rabbits-what-are-the-choices/