Bitvise SFTP is a third party software, and is deemed out of scope for GCP support. However, We will always try our best to assist you in any way possible.
This is a
google general document for connecting to instances using third-party tools. Also I was able to find some
third party film with the title “FTP/SSH/SFTP Google Compute Engine with Bitvise, easy to upload files without opening port”. However, as these are a third party links, Google cannot guarantee the validity of the information they contain.