Setting up CORS policy for integration lambda

Hi I am using lambda integration for endpoint exposed via API Gateway but when I hit the endpoint I see the CORS Access-Control-Allow-Origin is not set from browser.

I will paste what I tried,
this is response template

#set($body = $input.json('$.body'))
#set($statusCode = $input.json('$.statusCode'))
#set($Integer = 0)
#set($context.responseOverride.status = $Integer.parseInt($statusCode))
#set($origin = $input.params("Origin"))
#if($origin == "" || $origin == "") 
#set($context.responseOverride.header.Access-Control-Allow-Origin = $origin)
    handler: src/districts/district-handler.list
      - http:
          path: '${self:custom.pathPrefix}/districts'
          method: get
          cors: ${self:custom.corsOptions}
          **integration: lambda**
            passThrough: NEVER
            template: ${self:custom.requestTemplate}
          response: ${self:custom.responseHeaders}

request template is working fine but when I load the endpoint in browser it gives following error,

district-settings/:1 Access to XMLHttpRequest at ‘‘John’’ from origin ‘’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.

Does serverless config looks correct? Any help or suggestion is greatly appreciated