Configure alert when the number of HTTP 500 event exceeds threshold on InfluxDB Cloud 2?

I am using InfluxDB Cloud 2. I am sending my nginx logs and the logs include the server’s HTTP response code (200, 404, 500, etc…) as a measurement.

However, the alert UI forces me to use the “Query builder” and I cannot switch to the “Script editor.” I can’t find any way to filter based on value of _value.

I assume the correct filter will look like this? How do I enter this filter in the alert UI?

|> filter(fn: (r) => r._measurement == "code" and r._value == "500")