How to calculate overall V2G score from BigQuery file (variant_gene)

I was wondering why the column overall v2g is missing from the variant_gene file from BigQuery open targets genetics repository and how is it possible to calculate it ?
I am using a query to intersect the v2g results for my GWAS datasets and i need to include also the column for the overall v2g score.

Can you give me an example of the formula for a variant? How the overall v2g score would be calculated manually from the columns available in variant_gene file from BigQuery ?