FUNCTION_NOT_FOUND: line 1:8: Function 'dateadd' not registered

If you're using the latest version of the Athena query engine, it uses Trino underneath, and the function is date_add (with an underscore): https://trino.io/docs/current/functions/datetime.html#date_add

You'll find links to all the functions supported by Athena's different versions in documentation: https://docs.aws.amazon.com/athena/latest/ug/functions.html