From Windows tot apple on a MacBook

ios is only for mobile devices macbooks run what is called MacOs

if the friend has windows installed in bootcamp on the macbook then when one boot up the computer

holding down the option key should provide an option to choose if it's to start macos or windows

try reading

Start up your Mac in macOS or Windows with Boot Camp – Apple Support (UK)

Before proceeding, ensure any important data on the MacBook is backed up, as reinstalling macOS may erase existing data.