For me personally speaking I didn't train myself to wear diapers, it just happened because of medical and psychological issues (see my earlier replies).
How ever I have some tips that may make it easier for you
First step: Buy or acquire some diapers in your size choose the most absorbant possible for nighttimes you don't want any accidents.
Second Step: make sure you have complete privacy there's nothing worse than getting caught by a family member or neighbour, as it's embarrasing.
Step three: Start wearing diapers 24/7, or as much as practically possible remember they are there for a reason, don't forget to drink plenty of fluids it's no fun being rushed to hospital severely dehydrated.
Step four: fall asleep naturally just relax and the rest should follow your body will remember what it was like as a child even if your mid dosent.
Step five: listen to baby stuff as in Nursary Rhymes watch baby cartoons on YouTube and learn to fully regress back to your childhood get yourself pacifiers teddybear and childish stuff if you have money.
Step six: tell yourself you need diapers and avoid going to the toilet unless you have no other choice as you can change yourself in there just don't use the toilet.
Step seven: Chpose wisely who you tell, If you need to tell pepole you need diapers tell them honestly that you have a ligitimate disability and your not a pervert then there will be less prejudgment
as there are other pepole in the same boat figuratively speaking.
Step Eight: plan for the longer term stock up on diapers and everything you need get a carer or nanny if needed someone who is sympathetic is much better than someone who is not ajust your house or home if nessisary have someone build you a nursary and if that's not possible find one that is safe and that caters for adults or paraplegic pepole if you don't like the stigma of porn.
Step Nine: Be yourself don't ever try to be something your not, as long as your not hurting anyone or doing anything illegal than you have nothing to be afraid or ashamed of try taking each day as it comes it takes patience and time to fully retain yourself, however keep in mind once you start it's for life not just a fad as it's irreversible in the longer term.
Step Ten: After a few week s or even months in diapers your body will ajust to its new reality if you want to continue do so at your own choice or discression but of you get this far than your life will have changed.
Yours sincerly
China baby888.