Hi Gianluca Maggiolaro,
once you downloaded the AddOn from the Download section of the Praim’s website you have to add the package on the Package Repository, see https://wiki.praim.com/display/ThinMan/Package+Repository+Menu for more information. The package is in the “Praim Archive” format.
Then execute on the thin client a firmware update operation (right click -> “Firmware Update”) and when prompted select the AddOn package from the repository.
What do you mean with “How has to be the ThinMan configured?”.
In general it is important that the thin clients know the ThinMan Server address. Read this chapter https://wiki.praim.com/display/ThinMan/How+to+Setup+ThinMan+Address+on+Thin+Client that I hope will help you.
For other information read the wiki above or place another question in the Expertt Community.