BigQuery is a scalable, managed data warehouse tool available from Google (see https://cloud.google.com/bigquery for more information).
The first step to import data from BigQuery, as with any external connection, is to create the data connection in LityxIQ. See https://support.lityxiq.com/277108-Data-Connections for more information on creating and managing external data connections. Note that when setting the connection settings for BigQuery connections, you will need to know the BigQuery Project Id where the data you will use resides. See BigQuery documentation for more information on finding the Project Id.
The second step is to import raw data from a BigQuery table. Since BigQuery acts much like a standard SQL database with respect to how one interacts with it, importing data is much like importing data from other SQL databases in LityxIQ. See https://support.lityxiq.com/096794-Import-Data-from-a-SQL-Database-Table for more information.