Hello @ketanaga ,
Note: make sure you share the complete ThingWorx version number in future, there are some small differences that may matter.
Going back to your issue: I presume that you use a version of ThingWorx below 8.3.3. In this case, you will not be able to find those connection strings in that subsystem, and you need to insert your appKey in the zip file itself.
The answer is found in the Help Center article that @raluca_edu shared. Look at the section "Using the Google Widgets 3.0.1 and Earlier Versions" , it's at the end of the article. The widget is also different - you need to use the 3.0.1 Google Maps widget from the marketplace.
PS: I want to use this occasion to remind you that ThingWorx 8.3.x will be out of support in 8th of June 2020. Ideally you should migrate to the latest ThingWorx version to gain advantage of the newest features, bugs and security fixes. I believe version 9.0 is planned to be available June 2020 (https://support.ptc.com/cs/product_calendar/PTC_Product_Calendar.htm )