Hey!

yes, if you do not have certificate then you can act as a general category candidate and so, you can fill out the form as per general category candidate. But if you want to take advantages of being an OBC candidate then you must get caste certificate issued by the authorities, for this kindly visit the state/district portal and if you come under OBC-NCL category then you need to issue the certificate by central government only.

Hope I answered your query, thankyou!