Congratulations! And thank you for sharing the news that recovery is possible.
Mood disorders (including depression and bipolar disorder) usually have many causes or contributing factors: the genes you were born with, positive and negative things that happen to you, your physical health, and substances you put into your body. Symptoms of depression or bipolar disorder are not a yes/no thing (like being pregnant, where either you are or you are not). Instead, symptoms of mood disorder are like high blood pressure. Some lucky people are born with a very low tendency to high blood pressure. But some people are born with a higher risk. Whether or not that risk comes out as high blood pressure depends on lots of other factors in your life (diet, exercise, stress, etc). And even if you develop high blood pressure, you can bring it down over time by working on those other factors. In the same way, you can certainly reduce symptoms of depression or bipolar disorder by making positive changes in your life: working to avoid or better manage negative events or stress, avoiding alcohol or drugs, increasing your physical activity. So positive life changes can certainly change the chemistry of your brain and reduce symptoms of mood disorder.
Some people refer to bipolar disorder as a chemical imbalance, and that term has both positives and negatives. On the plus side, that term reminds us that bipolar disorder is a serious illness and not just a moral weakness or character flaw. But on the negative side, that term can sometimes give the impression that there is nothing you can do to change the way the illness affects you. Recovery is hard work, but it is possible.