I do not know where this information is stored but customisation is stored in the normal.mxt template. Often when ArcMap plays up then deleting this template does a "factory reset". On the next start up of ArcMap the normal.mxt is recreated.
WARNING: This deletes ALL customisation, so any toolbars or addins you have added and any corporate customisation of the interface is lost. So you have to be 100% sure you want to remove this file, normally people rename it and if the removal of the template did not fix the problem then people can reinstate the template.
On my computer, which is running ArcMap 10.6 the template is here:
C:\Users\xxxx\AppData\Roaming\ESRI\Desktop10.6\ArcMap\Templates
xxxx = is your profile name
I can't promise this will work as maybe the locator information is stored elsewhere? Having just written this I noticed that there is a folder called:
C:\Users\xxxx\AppData\Roaming\ESRI\Desktop10.6\Locators
May be that is where this information is stored?