What kind of changes?
"For accumulating 20 hours of held-breath underwater swimming within 3 weeks from start to finish– 10 or more points I.Q. gain; better span of attention; better span of awareness; better awareness of the interrelatedness of things and of ideas and/or perceptions; finding yourself way better at winning arguments or disputes!"
It should go without saying this is nonsense.
This article makes a lot of claims about I.Q. scores before and after holding breath (specifically underwater, for some reason), but there are no links to studies, no mention of who or how many people participated, etc.
This is the definition of a baseless claim.