In some ways coding is like really risk free surgery. In a code base known to work, the developer moves incrementally and safely around the system, always checking that the patient is still able to function and always trying to keep the system a build or two away from usable.
Focus on one thing at a time, avoid the temptation to make parallel changes, unless you are really really good.
If these changes don’t work each time, then you have your answer.
You can take a look at our work on Google Play