Custom WCF Service and MaxReceivedMessageSize

I deployed a custom WCF REST service (a file uploader) into ISAPI folder. I am able to call this service successfully using jQuery client. I followed this article to develop WCF service: https://social.technet.microsoft.com/wiki/contents/articles/24194.sharepoint-2013-create-a-custom-wcf-rest-service-hosted-in-sharepoint-and-deployed-in-a-wsp.aspx

Issue is that WCF service is unable to accept any files over 64KB.

I understand that I need to increase MaxReceivedMessageSize property for this service. However, I am confused as to in which web.config I need to make this change. I see a web.config in ISAPI folder or do I need to create a new web.config? If I scroll through ISAPI web.config, I do not see any endpoint for the WCF service.

Here is the svc file:

<%@ ServiceHost Language="C#" Debug="true"
    Service="FileUpload.ISAPI.UploadService, $SharePoint.Project.AssemblyFullName$"
    CodeBehind="UploadService.svc.cs"
    Factory="Microsoft.SharePoint.Client.Services.MultipleBaseAddressWebServiceHostFactory,
    Microsoft.SharePoint.Client.ServerRuntime, Version=15.0.0.0, Culture=neutral,
    PublicKeyToken=71e9bce111e9429c" %>

Any pointers?