Bubbles in Secondary Fermentation of Wine

Hi im totally brand new to wine making and ive been making a batch of Strawberry Banana wine but ive got some questions. I started off with a specific gravity of about 1.080 and after about a week and a couple days I was down to 1.002. I racked it into my secondary fermenter and had about a whole bottles worth left over and didnt want to waste it so I used a bottle as a makeshift secondary fermentation vessel. Im mostly worried about the bottle since I dont want to let it get too much oxygen and it dont have an airlock for it so ive mostly been using the bottle plug pushed in about 75% of the way to vent a bit of the buildup inside. Anyway its been about a week in a half since then and the bottle is still bubbling and im worried about if I should be leaving the plug completely in and releasing the gas periodically or if I should be leaving it 75% in and letting it vent normally. Are these bubbles still just from left over fermentation that is still active or are they just bubbles naturally being let out of the liquid over time? Should I be cold crashing the bottle now or later, all various questions I have. I Thank you very much for any answers you can give.