step 1: go to double rainbow, get pearl milk tea
step 2: go to wonderful foods, get pearl milk tea
step 3: throw away the tea from wonderful’s pearl tea and keep the pearls in the cup.
step 4: strain the tea from double rainbow’s pearl tea into wonderful’s pearls.
step 5: enjoy good pearl milk tea!
You could always request to buy only the pearls (usually they give you a cup full!) and likewise buy milk tea without pearls. Well but doing that won’t make that interesting a story. =P