It is possible to zoom in/out on the puzzles you are working on. This option is available for puzzles of 140+ pieces. When you start a puzzle, it automatically opens already enlarged in a certain area. However, you can change it and make the puzzle smaller or enlarge it again by tapping on the Scale button.
Please note that there is no option for changing the enlarged area of the puzzle – it is done automatically. You will be moved to the next part only when you fully complete the first part.