And if you mean you lost the hotspot functionality, you have to re-install the hotspot package: Just upload the correct package file to the router (by FTP or SCP) and reboot...
This is just necessary when you are effectively MISSING the hotspot package. You can check this by looking at the installed packages. If this list doesn't contain the "hotspot" package, you don't have hotspot functionality. Then you have to upload the hotspot-2.8.24.npk to your router and reboot to install this feature package. Of course you can also upgrade to 2.8.28 (recommended...) by upload the "all packages" package and reboot (if your license still permits updates)...