You will need:
Step 1 Lay your underwear on the hemline of the tank top.
Step 2 Cut two slits, don't forget the hem allowance
Step 3 Place the underwear on the widest of your tank top
Step 4 Cut from the slit all the way up
Step 5 Outline the front panel with pins. Place your fingertip on the hemline and pull the fabric away. Pin the pin down.
Step 6 Take out your pins and pin only the front of the top. Then fold your top in half and replace the pins on both sides of the tank top.
Step 7 Cut along the pins.
Step 8 Try on the bodysuit to how it looks on. Shorten the front panel if you can
Step 9 Hem the edges with a zigzag stitch. Then sew the bottom or place press studs.