You want to use Partner Interconnect to connect your on-premises network with your VPC. You already have an Interconnect partner. What should you first? 

Answer options:

A. Log in to your partner`s portal and request the VLAN attachment there. 
B. Ask your Interconnect partner to provision a physical connection to Google. 
C. Create a Partner Interconnect type VLAN attachment in the GCP Console and retrieve the pairing key.
D. Run gcloud compute interconnect attachments partner update <attachment> / --region <region> --admin-enabled.

B

Reference: https://cloudplatform.googleblog.com/2018/06/Partner-Interconnect-now-generally-available.html