The
Quality Check Plugin

will do this (after you configure the setting)
1) Right click the PI Icon: Customize: <set the author initial format> (1 time only)
2) run the PI. Check Metadata: check author initials. This identifies all the books that fail your setting
3a)Select the ones that need fixing (

Ctrl-A if done following step 2 )
3b) run the PI: FIX: Author initials