|click on menu|TEMPO_MENU_NAME| not working in FitNesse 19.1

This was happening for me as well on 19.1. 

If you see the log files you will see exceptions as per below.

ERROR com.appiancorp.ps.automatedtest.exception.ExceptionBuilder  - Tempo Menu - Actions
org.openqa.selenium.TimeoutException: Expected condition failed: waiting for presence of element located by: By.xpath: //div[starts-with(@class, 'SiteMenuTab') and contains(translate(text(),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefghijklmnopqrstuvwxyz'),'actions')] (tried for 10 second(s) with 500 MILLISECONDS interval)

Now if you check the class for the menu options on your browser it still appears as - appian-menu-item and not SiteMenuTab.
In the jar file - fitnesse-for-appian-19.1.2.jar you can find the metadata.json where  entries for various elements are define - mostly xpaths.

The file contains two entries for xpathAbsoluteMenuLink one for version 7.10 (which mentions appian-menu-item, the correct one) the other one is mentioned under version 19.1. Remove the one from 19.1.

Can you brief in detail .. how to browse the files to edit the entries  

you can use 7-zip, drag and drop files in the window once edited

you can use 7-zip, drag and drop files in the window once edited