You could use the SCOBY and raw kombucha tea. High Country would be a better choice, but GT should work--although I would try to not use flavored if you have a choice. The flavoring itself shouldn't harm the culture, but the sugars will throw off your recipe.
You can also use your SCOBY and a tiny bit of the starter or cider vinegar and simply build up your brew again by starting small and then adding more sweet tea once that has reached the right PH.
I also have a giant SCOBY I let go too long. I used a little of the culture and some of the starter and added to a new batch. Once that produced KT I added more sweet tea and the giant SCOBY and got things back on track.
Tap: DIPA, oaked Baltic porter, XXX pale ale, dark IPA
Bottle: vanilla kombucha, oaked puh-er kombucha, blueberry kombucha,
Primary: rose hip kombucha, oaked honey and oolong kombucha, hopped kombucha brewed with green tea infused with cab. grapes