Before we start, are you sure that you’ll need to adjust Arum? Due to its shape and grown on sleeves, this dress fits a wide range of silhouettes and you might not even need to modify it, even if you are a D cup or higher. Check this by making a muslin corresponding to your bust measurements.
If your muslin is loose at the shoulders, but too tight at the bust, a FBA is indeed needed. To do this, we will be adding a bust dart to the dress.
Put on your muslin, or pin the pattern (#1 – dress front) on you, and mark the position of your bust apex, as seen on the picture above.
Draw three lines on your pattern starting from this point: one that meets the shoulder line, one vertical line parallel to the center front line, and one that meets the underarm curve.
Slash through these lines, being careful to leave two pivot points as shown on the above drawing. Open the vertical slit the amount you want for your full bust adjustment, making sure that the side of the pattern stays parallel to the center line. You’ll notice that the hemlines at the center and the side of the dress are now uneven. Cut the center piece along a line perpendicular to the grainline, and align the lower piece so that the hemlines are on the same level.
Overlay a new piece of tracing paper on your pattern piece, and trace the outlines of you new dress front. Draw the dart created by your changes: the dart ends correspond to the extremities of the slashed part of the underarm curve, and the tip should be 3cm to the left of the bust apex. Finally, shift the pocket placement to the left of half the amount that you added to the front.