Step 1: Confirm that Gopher for Users is a whitelisted app on your domain, and that your user accounts are authorized to install it.
As a G Suite super admin, under Apps > Marketplace apps > Settings for Marketplace Apps> Manage access to apps, confirm that users in your domain are allowed to install whitelisted apps from the G Suite Marketplace.
Next, whitelist Gopher for Users within the Google Marketplace Apps settings. To do that, navigate to Apps > Marketplace apps > Whitelisted Marketplace apps. Select the + icon in the right hand corner and search Gopher for Users. Check the box next to our add-on and select Whitelist, then Confirm.
Step 2: Install the Sheets Add-on from the G Suite Marketplace
In Google Sheets, start by going to Add-ons > Get Add-ons. Search for Gopher for Users and select Individual Install.
Or, cut to the chase and install it directly from here.
Once installed, you can open Chrome Gopher from any Google Spreadsheet from Add-ons > Gopher for Users > Launch Sidebar
It is important that you do NOT install the Add-On domain-wide as it will appear for ALL users.