you need to change it on the ini file and on the "
\apps\wiiflow\meta.xml" (USB and SD if you use them), on section
Code:
<arguments>
<arg>waitdir=usb1:/apps/wiiflow/wait_imgs</arg>
<arg>waitloop</arg>
<arg>ios=249</arg>
<arg>noflash</arg>
</arguments>
You must to consider to read the thread here about cIOS, you really only need the cIOS 249 preferable the d2x v8 (or d2x v10 which are the same of v8 only the version was bumped to the avoid the conflict about the vWii ones) and for slot 249 you should have it based on IOS 57 which have the most compatibility with games, for some very few "problematic" games you also can have the slot 250 with d2x V8 base IOS 56 and use only on Wiiflow's game setting no anywhere else.
more information on:
https://gbatemp.net/threads/ciosx-rev21d2x-yet-another-hot-fix.277659/
and
https://gbatemp.net/threads/d2xl-cios-a-fork-of-davebaols-d2x-cios.558581/post-8968173 (
a thread about cIOS for Wii Mini but this post include a very useful explanation about the cIOS, their use and setup; a must read post)
If you can not boot on wiiflow try to boot to Homebrew Chanell and use any installation method you like to change your IOSes.