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