This t-shirt refashion can be done by cutting the center back out, cutting the piece to narrow strips, making holes on the back edges and tying the strips on. For longer strips you might need to cut up also another t-shirt.
DIY tank top - item: scissors, bleach, plain tank top/t-shirt. Dip dye the bottom of the shirt with bleach. Wash it out and let it dry completely. Then cut the part you bleached into thin strips and tie a knot at the ends.
25 DIY T-Shirt Cutting Ideas To Try On Your Old Outfits For New Look
DIY Tee to Cut Out Bandeau Top Tutorial from Bleached Faded here. Really easy tutorial although Id probably sew wear she has used fabric glue. I would also again wear a tank top or something under it so it's more modest.