Pre-wash and dry your mask according to package directions. If there are no directions, machine wash warm, and let air dry.
Thread a sewing needle, and then pull the thread halfway through so it is doubled onto itself. Tie a knot at the end of the thread.
Find the center of the top edge of the mask. For contour masks, there is usually a vertical seam running down the center.
Poke the needle through the back of the mask at the center point, just below the horizontal row of stitches that runs along the long top edge of the mask. Pull it tight until the knot is against the fabric. Tack the nose bridge onto the outer layer of the mask by centering it where you pulled the thread through. Then insert your needle right next to the opposite edge of the bridge, and pull through to the back.
Repeat Step 4 two more times.
With your needle now pulled through the back of the mask, weave your needle under the stitches three times, then knot it. Cut off the excess thread.
Knot the end of your thread. Use one hand to hold the bridge securely at the center point of the mask, and use your other hand to carefully smooth the fabric towards one of the ends of the metal bridge. Starting from the back side of mask, pull your needle up through the layers of fabric and through the hole at the end of the nose bridge. Make three stitches that go up over the top edge of the metal piece, and three stitches that go over the bottom edge of the metal piece. With your thread on the back side of the mask, weave it 3 times through the stitches, and then make a knot. Trim the excess thread.
Repeat step 6 on the opposite end of the metal bridge.
Put on your mask. Press down on the nose bridge to shape it around the bridge of your nose. The fabric should now rest snugly along the top of your nose, and down towards your cheeks.
Wash and dry your mask again before wearing.