Adding a New Item
To add a new item to existing financial plan, click on the "…" button in the top right corner and then select "Edit Financial Plan". After that, you will be able to add new items to your plan or delete existing ones.
If you see that the app is showing unplanned expenses or income for your plan, you can add a new item directly from that screen. All you need to do is to select an unplanned item, enter its amount and add it to the plan.
Adjusting Existing Item
When looking at your plan, you can select its item and adjust its amount. To do that in macOS, double click an item. In iOS just tap on it once. You will have an option to either apply a new amount just to the current plan month or also include the following months as well.
Sometimes it can be very useful to add a comment to a particular plan period item. For instance, you know that in a particular month something has affected your spending and you should have planned for it. Adding a comment to that plan item will help you to easily see what has happened.
Plan items with comments in the Mac app have a blue triangle in the bottom right corner (in the table view mode).
A Word of Caution
While it is very easy to adjust a financial plan on the go, I recommend being cautious about that. You can find yourself making adjustments for every unexpected increase in expenses which defeats the purpose of having a plan.
Before adjusting a plan, ask yourself a question: "Was it reasonable for me to plan for that from the beginning?". If the answer is yes, then make an adjustment. Otherwise, leave it as unexpected spending.