You can start the training process by moving your feline friend’s current litter box into the bathroom, which should not be close to the toilet. Over the course of a few days, slide the box closer and closer gradually until it is alongside the toilet.
You can place the litter box on the top of a sturdy table near to the toilet if your cat seems good with this. You want your feline friend to get used to jumping up to do its business. You should continue this task for a few days, toilet lid up, seat down, just in case the cat starts jumping on the toilet seat itself
You should sprinkle fresh cat nip on the toilet seat and the table to encourage the cat to check out things. You can replenish as needed.
You should leave the toilet seat up and flush it regularly. Remember that you work for your feline friend and smelly toilet could bring back that amnesia
You can also search for a commercial product that is designed to toilet train cats if things do not work out. If that does not work, you can buy a bigger litter box