In Windows 10 the indexing location rules are stored in the registry at the following location:
(in win 8 or lower it could be in a neighboring location, rest of the instruction would be same)
To reset the indexing location rules to their default, delete this key. (backup)
Deleting it however might not be straight forward, it'll give an "access denied" error, as there might be some services using it. Best way to edit this registry is through Windows Recovery Console environment which can be accessed via
Settings > Update & Security > Recovery > Advanced Startup > Restart now then
Troubleshoot > Advanced options > Command Prompt
When it restarts and the command prompt opens up, type in
regedit to open the Registry Editor.
However the registry loaded here by default, as well as the the
C:\ drive, will not your actual one, but that of the Recovery Console environment's.
Your actual System Drive should be
E:\ or something. In the next steps you'll be able to browse the drives via Open File Dialog, figure out by your drive label, or files
E:\Users\<your account name> which drive is yours. The registry on it should be in
E:\Windows\System32\config directory, containing specific files (or "hives"), of which you want the
So in the Registry Editor's left panel, select
HKEY_LOCAL_MACHINE and then goto
File > Load Hive and locate that
E:\Windows\System32\config\SOFTWARE. It will ask for a name under which to display the loaded hive, just type in
SOFTWARE_real or something.
Then delete the above mentioned registry key from its new hive
That's all, close it, exit, and restart normally. It will recreate the default registry values in the place of the deleted one and Indexing Options should now have those default Locations.