You (or your Administrator) will need access to GCP to start with. Once the logs are forwarded you will see it in SIEM.
You will need to make change in GCP Console --> Security-->Google SecOps--> Ingestion
On this tab Enable -
1.Google Cloud logging
Ingest and analyze data from Google Cloud Logging.
2.Cloud Asset Metadata
Ingest and analyze data from Google Cloud Asset Inventory.