Lab contain Missing field

Hi
Hope any one can help to resolve an issue I have encountered. I am attempting the first Lab for Observability where I need to start my heartbeat.yml. Anyone can advise on the error message below?

INFO instance/beat.go:299 Setup Beat: heartbeat; Version: 7.9.1

INFO [index-management] idxmgmt/std.go:184 Set output.Elasticsearch.index to 'heartbeat-7.9.1' as ILM is enabled.

ERROR instance/beat.go:951 Exiting: error initializing publisher: missing required field accessing 'output.Elasticsearch.hosts'

Exiting: error initializing publisher: missing required field accessing 'output.Elasticsearch.hosts'

Regards
Lin