How do I delete (drop) Influxdb2 measurements in Node red

[Buckskin]

Did you actually call the bucket 'bucket' and the Organisation 'organisation' or are they just demo names?

Try something like;

influx delete --bucket bucket \
  --start '1970-01-01T00:00:00Z' \
  --stop $(date +"%Y-%m-%dT%H:%M:%SZ") \
  --predicate '_measurement="khdiff"'

Untried but in influx docs