How to shuffle teams in child competitions each season?

[Champol]

Hi, I was wondering if someone could help me with this one:

I am creating a piramid league system with advanced rules, with 1 first division, 2 second divisions (2A and 2B) and 4 third divisions (3A, 3B, 3C and 3D).

Everything works so far, except that all of the teams that are relegated from the 1st div. end up in 2A, (and only 2 out of the 8 teams that are promoted from the 3rd div. end up in 2A), and all of the teams relegated from 2A and 2B end up in 3A.

For now, I just want that all the teams in a parent division get "shuffled" into their child divisions each season, but I can't find out how to do it (I'm not using geographic boundaries and I don't want to, just random). Do you have any clue?
Thanks!

Edited June 26, 2021 by Champol