Step 1: Confirm that Gopher for Groups 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 Groups 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 Groups. 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 Groups 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 Groups > Launch Sidebar
It is important that you do NOT install the Add-On domain-wide as it will appear for ALL users.