To scale up to bigger volumes we recommend following the Mad Millie How to Guide for Kombucha and making 1 L (1 US qt) to begin with to 'wake up' your scoby.
As your scoby has been sitting dormant for a while it will need a good strong brew at 1 L (1 US qt) volume to get it going.
Once this brew has been made add the whole 1 L/1 US qt batch into a bigger vessel and use this as the starter culture. Then proceed to add your cooled, sweetened tea and follow the usual fermenting instructions.