We isolated a compound from plant source and got the structure but we are unable to find the class of it. please suggest any database or online tool is available to get the class of natural products?
Try a structure search? Note that some compounds may be in several classes. Flavanoids may also be phenol (due to OH attached to a benzene ring). Cumarin is also a member of the benzopyrone class. Look at similar compounds and see their descriptions with respect to chemical class in the literature.
To find these compounds, I read a few qualitative tests and color tests in the papers, I have done in previous work, if you want to give them the protocol.