The NavTiles Tools menu has some useful features to help you create NavTiles. It can be found in the top menu bar under Tools > NavTiles.
The NavTiles tools menu.
Create NavTiles From Sprites
When selecting one or multiple sprites, you can use this feature to quickly create NavTiles for each of those sprites. This automatically assigns each sprite to its corresponding NavTile.
Convert Tiles To NavTiles
This option is useful when you have already started working with Unity's Tiles. Using this feature, you can convert all your existing Unity Tiles to NavTiles. All data will be preserved, along with an added Area Index field.
CTRL+Z is not supported for Tile > NavTile conversion. You can use this option to undo a NavTile conversion manually. It will revert the selected NavTiles back into Unity Tiles, preserving their properties.
Create NavLinks for Tiles
Unity's 2d-extras package introduces extra tiles that can be used with a Tilemap. To use these special tiles in conjunction with the NavTile asset, select them, then click this option to setup NavLinks for them. A NavLink assigns its referenced tile with an Area Index, much like what happens when a Unity Tile is converted to a NavTile. NavLinks can also be used to assign an Area Index to custom Tiles.