Index network drive in MacOS, or reindex / rebuild index

So straight from Apple's mouth:

https://support.apple.com/en-gb/HT201716

1. Choose Apple menu  > System Preferences, then click Spotlight.
2. Click the Privacy tab.
3. Drag the disk or folder that you want to re-index to the list of locations that Spotlight is prevented from searching in.
   Or click the add button (+) and select the disk or folder to add.
4. From the same list of locations, select the disk or folder that you've just added. Then click the remove button (–) to remove it from the list.
5. Quit System Preferences. Spotlight will re-index the contents of the disk or folder. This can take some time, depending on the amount of information that is being indexed.