create a bucket if you don't have one, run
gsutil mb -p [PROJECT_NAME] -l [LOCATION_NAME] gs://[BUCKET_NAME]
Describe the sql instance you are exporting from and copy the sa
gcloud sql instances describe [INSTANCE_NAME]
Add the service account to the bucket ACL as a writer
gsutil acl ch -u [SERVICE_ACCOUNT_ADDRESS]:W gs://[BUCKET_NAME]
Add the service account to the import file as a reader
gsutil acl ch -u [SERVICE_ACCOUNT_ADDRESS]:R gs://[BUCKET_NAME]/[IMPORT_FILE_NAME]
Import the file: gcloud sql import csv [INSTANCE_NAME] gs://[BUCKET_NAME]/[FILE_NAME]
--database=[DATABASE_NAME] --table=[TABLE_NAME]