teaching bottom wiping

[Hamandcheese]

Struggling with toiletting for DS1 (no dx, but prob AS and / or dyspraxia). All a bit of a problem. Anyway, we are vaguely going in the right direction with the knowing he needs to go and gettting to the toilet and / or at least telling someone and / or (if outside) pulling down pants and weeing in the garden / field etc. Prob 1 - 2 wee accidents per day and 1 - 2 poo accidents per week.
But all still pretty heavily adult-supported.
I will soon need to teach him to bottom-wipe after pooing. ATM I clean him up myself using baby wipes as he bends over.
I have no idea how to go about teaching him to do it himself: what position (arm through legs or round his back?) how/whether to practise? He has relatively poor balance and proprioception and refuses to try to do things he finds hard.
If you guys can give me some starting point, I think I'll be able to get going. ATM I'm ignoring the issue, but I really want him to get it in the next yr or so...