Choose which Navbar type you'd like:

Pixel Navbar Icons.
Nexus Navbar Icons

Make sure your phone allows installation of APKs from unknown sources. Download the desired APK from above. Reboot your device. You should now see your new Navbar icons. If you ever want to revert back to the Samsung Navbar icons, simply navigate to Apps in settings and Uninstall: Com.android.systemui.product.res.Overlay

Source: XDA