You need access to appropriate information that would help you identity the substance.
Hopefully you have a pure substance, such as an element or compound, or a standardized substance. If so, you would have to do research and consult tables and charts. If the density was determined in an experiment, the instructor should provide a list from which to choose. Remember that temperature affects density.
A sample of an element was obtained by a student. After making the appropriate measurements and calculations, the density at
The list included a density of