Why would you want to do that? If things don’t work, restart the device every now and then. Other than that the operating system assigns RAM as needed, like most modern computers do.
As usual with these posts, nothing of any use is ever given as details, but I’m wondering if he actually means the storage rather than the RAM?
I’m running on 2gb out 64gb on my iPhone XS ….what my options iMac @ home….look for space on my iPhone XS….insight please….