Assuming that you’re referring to a lead you received from Yelp, and the same lead contacted you again from Google, or vice versa. So, the attribution issue is within your internal systems.
Within your CRM, you can add the source and use the first channel as your primary source. For example, say a lead contacted you first via Google LSA, you add that as the primary source. When the same lead contacts you again via Yelp, you can ignore it.
Similarly, these settings can be done if you’re using reporting tools like GA; most of these tools show the first source of the traffic and can assign attribution to that.