Gel polish can become thick if it has been sitting unused for a while. To restore its consistency, try gently rolling the bottle between your hands for about a minute. This helps warm up the polish, making it thinner and easier to apply. Avoid shaking the bottle, as this can cause bubbles and affect the finish.
If the gel polish remains thick, you can also try running warm (not hot) water over the bottom of the bottle for a few seconds. This will help to soften the polish, making it more fluid.