Reddit mentions of Revlon Concealer Brush, Premium

It takes time and patience to achieve these kind of nail styles. The two most important products you need to have of you want great nails are acetone and a small tapered brush (a concealer brush works best). Don't buy a cheap brush because the acetone will eat through the glue quickly and it will fall apart. I've had this one for years and the bristles are still perfect.

Use the brush and acetone to clean up the skin around your nails and quickly fix mistakes. Acetone removes polish immediately and cleanly, unlike non-acetone polish removers.