NavCash can be downloaded from the NavCoin website. After the App is downloaded, simply follow the wizard to finish the installation.
To use NavCash with Ledger Nano S, an App loader is needed to be manually installed on Ledger since the Ledger App is still being reviewed by the Ledger team. The loader can be found in the link for the NavCash wallet above.
Ledger Nano X is not supported at the moment since it does not allow 3rd party App.