It can happen that YAMM menu doesn't load properly. This is just a temporary issue and in general it is automatically fixed within a few seconds.
What should I do?
If you can only see 'Help' under Add-ons > Yet Another Mail Merge, it is usually an issue related to Google Sheets.
Sometimes, the menu doesn't load properly. In most cases, this is only a temporary issue. If you encounter this, simply refresh your spreadsheet, wait a few seconds, then try YAMM again.