You cannot see the Add Ins tab in Excel, although you have Add Ins installed.
Disabling and re-enabling all Add Ins installed in Excel resolves this issue.
1.) Open Excel
2.) Click on File (top left corner)
3.) Select Options in the File menu
4.) In the Options dialog, select Add-Ins and on the bottom of the dialog, click the Go button next to Manage: Excel Add-ins
5.) On the Add-Ins window, uncheck all Add-Ins and click OK.
6.) Follow steps 2.) to 4.) again to get back to the Add-Ins window, and check all the Add-Ins again. Click OK and you should see the Add-Ins tab in Excel.