Win10:
You have to back up your old Postman
C:\Users%user%\AppData\Roaming\Postman\IndexedDB
Then copy it to the same location of the new Postman installation.
On Mac: The json files were automatically backed up (/Users//Library/Application Support/Postman/backup-YYYY-MM-DDTHH:mm:ss.SSSZ.json) but it is not documented anywhere.
You just have to reimport them
In Debian-like systems, using Postman v7, I found a backup of all the collections and environments saved as JSON in ~/.config/Postman with the prefix backup-.
If you weren't logged in to the app and using it offline or in the
Scratch Pad mode then your data won't get synced to our servers and
stays local to your instance. In this case, try following the steps
below:
Look for the backup files under the following folder:
%appdata%\Postman\for Windows ~/Library/Application
Support/Postmanfor macOS ~/.config/Postman for Linux
Backup file names will be similar to
backup-2020-02-26T23-13-43.082Z.json (date or time will be different
for you).
If you are using a snapped Postman on Linux, let me save you some time.
Copy all the content from your source snapped Postman UNDER (as the target GUID can be different)