If you made these changes to the Gridder files directly instead of using the override files that I recommended then those changes are lost if you update Gridder. This is not a unique limitation to Connections or its templates, the same would occur if you made direct edits to a WP theme or plugin.
Depending on your webhost…
Did you just very recently update Gridder? Like today? If so, you might be able to retrieve the edited files from your web hosts backup files for your site. You would have to contact them and ask specifically for the files in
../wp-content/plugins/connections-gridder/. The last thing you want is for them to restore the entire site. It’s my unfortunate experience that web hosts tend to mess that up, badly.
If you have no reliable backup files, the only option is to make all those edits again, but make sure they are to template override files instead. These will be safe from WP overwriting them when it applies updates.
Not sure how helpful this is, but I hope it is!