A boostrap for the wallet can be downloaded from:
https://bootstrap.nav.community/bootstrap.tar.gz
NOTE: this may take some time as this file is around 3.3GB in size
Once downloaded, you will need to use a program like winzip (tar/gunzip on linux) to extract the blockchain folders from this file.
You simply need to replace the chainstate and blocks folders inside your NavCoin data directory with the ones from your bootstrap.
To find the data directory please see this article
NOTE: If you get the error error opening block database, do you want to rebuild the block database?, this would indicate your download failed or the file did not fully extract.
Bootstrapping is the process of adding a pre-synced blockchain from a trusted source to your wallet, allowing you to skip part or all of the blockchain syncing process.