In LiveAgent agent panel navigate to Configuration > System > Plugins. Find the 'Desk.com Migration' plugin and click on 'Activate' button next to it.
Then you have to reload the agent panel. After reload go back to the Plugins section and click on 'Configure' button next to the plugin.
In the configuration popup you have to enter:
1. Desk.com URL - you have to enter the URL to your Freshdesk account, e.g. https://<DOMAIN>.desk.com
2. Username - email which you use to log into Desk.com
3. Password - password which you use to log into Desk.com
In the plugin configuration hit ' Save' and you are done. LiveAgent imports tickets from Desk.com in the background.
Here you can see tickets in Desk.com:
Desk's tickets in LiveAgent after importing: