Find the plugin that is rendering the hook, it has code within said plugin that will divulge the links its using.
- Take note of the code.
- Disable the plugin which generates this custom tab.
- Now in AdminCP > Settings > Navigation Manager > *Setup a new tab, use the link in the plugins code (change if required i.e. if some php code is inside the link simply snag what you know is the correct url for the mod its making the tab for) then save.
- Check to ensure the tab shows AND functions correctly. Don't forget to add in any sub-links if they existed on in the custom tab for the mod, this can also be done using the navigation manager.
Now your custom tab has returned yet at the same time its done in the new Navigation Manager instead of a plugin, its now up-to-date in regards to being properly included with all other navbar links in the actual navigation manager.