Using the Extension:

Open a new or existing Google Sheet™ 

If the add-on has been successfully installed you'll see a new menu option under Extensions: "Shared Print Lookup". Under this item select "Search by OCLC Numbers".  A side bar with options for searching will appear on the right hand side. Choose the tab name that contains the items you wish to search.  By default, the script looks for OCNs in Column A of the selected tab. 

If you are searching Shared Print Retentions in OCLC, choose which program you wish to compare against. Note that OCLC lookup requires an Worldcat Metadata or Search API Key.  See How to Request a WSKey if your library does not already have one. 

Select HathiTrust and/or Internet Archives if desired. No API key required. 

Enter an email address if you wish to receive an email when the search completes.  Note that emails may end up in your spam folder.

Select whether to allow the search to run for 6 minutes or 30 minutes. Free Goolge accounts will time out after 6 minutes, while paid accounts are allowed 30 minutes. 

The  search is limited to 10,000 rows. This is an arbitrary number designed to keep search from becoming unwieldly. The script can rarely get through more than 1000 entries in the 30 minute time limit. You will receive a warning if your search is more than 10,000 rows. 

Select the [Start Search] button.  If there is data that may be overwritten by the search, you will be alerted. A 'working' bar will appear while the lookups are being performed.  

Note the working searchbar also lets you know how long the script has been running. If the script continues to run beyond the time limit you choose, a red background will appear. This is an error condition that indicates the script has failed. Please let me know if this happens to you - it should not!

If the search times out before completing all the lookups, it will fill in the data to the row where it left off. You can restart the search at the appropriate row by entering it in the "Start search at row number" field.

Installing the Extension:

In a Google Sheet, us the menu path: Extensions / Add-ons / get add-ons, then in the Google Marketplace search for "shared print retentions search" and install