Well, this is often the hard bit, especially if you’ve manually created the tables using .csv uploads that you’ve exported from other SEO tools.
This process is fine once, but soon becomes a painful and tiresome exercise if you have to repeat this daily, weekly or just monthly.  You have to automate or suffer surrendering the majority of the benefits you will derive from using Big Query in the first place.
Using Big Query necessitates that you create a data pipeline that needs to be managed and monitored.  This requires a mid-level software engineer.  It’s not a big job but one that will take a few days to a few weeks depending upon how many data sources you are connecting to and the state of their APIs.
You need to consider how often each data source is updated.  For example, if you only pull in backlink data from Majestic once a month then that’s fine, but if you are checking new links across all your competitors daily then you need a better solution that uploads data daily.
You also should consider what happens if you change keyword tags or have other content that is updated multiple times a day; again, you will need the services of an engineer, as you need to stream the data to Big Query.
It's probably a lot faster and cheaper to switch SEO tool suppliers and let SEO platforms like Authoritas automate the whole ETL (Extract Transform Load) and maintenance process for you.