It is easy to make a claim based on another's acceptance of it. This occurs in many forms:
Each of these fallacies base the accuracy of a statement on acceptance from another person, group, or writing but does not provide any underlying evidence that the statement is correct.
Point out that your opponent's argument is dependent on somebody or something else's opinion, but they haven't shared any logical or factual support for the argument itself. Ask them to clarify what evidence they have for their claim besides someone else's acceptance of it. If they are referrencing a field expert that you can request that they share the experts credentials. With more controversial issues you may also need to discuss the experts underlying research or reasoning.