It is a common issue for females. Nails-paints became dry very quickly. How can I reuse my dry nails-paints?
Adding on to @user18894's answer, you could also buy acetone from a beauty shop or drug store. Dip the brush of the nail polish into a bit of acetone, then place it back into the bottle to make the dry polish runny again.
Here are some more suggestions and a step-by-step guide: https://www.wikihow.com/Restore-Thick-Dried-Out-Nail-Polish