Not all Lavender varieties do well indoors as houseplants - there's a guide here https://www.gardeningknowhow.com/edible/herbs/lavender/lavender-as-a-houseplant.htm about which types are more likely to, so which variety you bought may be part of the problem.
I cannot tell if the soil is dry or not, but the plant does have the appearance that suggests insufficient water (or too much) might have been a problem - that or being too near a heat source, or both. In damp or wet soil, they can succumb to fungal infections which kill them - poor airflow indoors does not help. Pick off dead leaves from the top of the soil - if it's dry, water it well, allowing it to drain down freely before replacing back on its saucer (I am assuming there are drainage holes in the pot), then let it dry out so the top of the soil feels quite dry before watering again. If its not dry, then let it dry out a bit before watering again.