Are you familiar with understood.org?
Here's a page of tips on cognitive flexibility from the website:
https://www.understood.org/en/schoo...ls/7-tips-for-building-flexible-thinkingAnother strategy, especially for social-behavioral situations, is to use social stories, for example, starting from one or two pictures that portray a common problem situation. Discuss with him some of the possible actions that the characters in the story could take, the possible outcomes, alternate solutions, etc.
There is also some research that suggests that having children do sorting games where they sort first by one element, and then re-sort by a different element, can help build some switching skills. For instance, games like Guess Who?. Or taking a set of animals and sorting by, say, number of legs, or size, or food they eat, or regions they live in, or cold/warm-blooded, etc. Or sorting plants by shape of leaves, or color of leaves, or venation, or number of lobes, or by flower shape, size, petal pattern, color, scent, etc.
