I haven’t made Kombucha but I’ve made milk kefir and for milk kefir it takes a couple cycles for the grains (equivalent of the scoby) to start growing and looking healthy after they’ve been sitting a while or their environment is changed (like a new brand of milk).
How long has the batch with the new scoby been fermenting? It has sugar to eat? I’d probably leave it be and see if the scoby starts to perk up.