If you want to get into the state as soon as possible, then I suggest looking for some completed budget and final accounts (the project is not big, but relatively simple), and then comparing them with the drawings of the construction site, especially with the budget quota (quota subtitle, measurement rules and related instructions), consulting experienced veteran comrades if you don't understand, and then trying to redo the budget yourself, the budget level will definitely be greatly improved within several times. Of course, at the same time, don't forget to read some related books, such as: cost engineer training materials, budget manuals, building construction manuals and so on.
The method I am talking about is the train of thought from practice to theory, and it is a shortcut to learn budget quickly. Of course, there are still many things that need to be enriched and improved, so it depends on your own efforts. You can take part in the training course for cost engineers, but after you finish it, you still have to do as I say.