If you have downloaded and extracted the .tar file, then in your computer you should have now a folder directory with this structure:
The entire chat history is saved in the messages.json file. Media files shared with Teams are saved in the \media folder.
The messages.json file is actually a plain text file where the data are encoded using the JSON format.
The official method to view this JSON file is by using the parser which you can download from this site.
https://go.microsoft.com/fwlink/?linkid=2133728
Using the index.html file from this parser, all conversations saved in the messages.json file are show in the browser used to open the index.html viewer.
You may search on the Web for another, better 3rd party JSON parser, but the application which I'm using is the vbExportViewer app. However, be aware that this app can only be used on a Windows computer.
Download this zip file (vbExportViewer.zip) from this OneDrive site:
https://1drv.ms/u/c/849db44edd75828c/UQCMgnXdTrSdIICE7fQAAAAAANpMMyJJIZ4Undo
Extract all files from this zip archive to 1 folder on your computer.
This folder should now contain these 4 files:
vbExportViewer.exe
ComDlg32.OCX
richtx32.Ocx
vbExportViewer.exe.local
It is important that all these 4 files are located in the same folder.
There is no installation tool, but in order to register the 2 .ocx files, it is required to run the first time (and only the first time) the vbExportViewer.exe file with the Run as Administrator option.
Right click on this file and select the "Run as administrator" option. This should open the viewer application.
Use the Browse button to browse and load the saved messages.json file. A list of all available conversations should now be shown in the All conversations box. Clicking on a particular conversation should open a window with all available messages present in this conversation. It is possible to have multiple conversations open at the same time in separate windows.
With this application, messages saved in the messages.json file are parsed to provide a more "human friendly" reading form incl. links to media files saved in the \media folder.
Conversations listed in the chats screen open in a separate window, and from there, the content of the selected conversation can be printed or saved to a file.