It's easy.
Just open the Tabs app > Home > tap "Extras" button > tap the "Restore" button and enter the same Apple ID, that was used for the original purchase.
If you still can't restore your in-apps, please log into the "Account" section with your Ultimate-guitar account. Your in-apps purchase can be linked to your Ultimate-guitar account.

Note:Tabs app for iPhone and Tabs HD app for iPad are not the same and require separate purchases.