Update Records with AWS Glue

I have two S3 buckets with data tables, namely A and B, and a Glue job, that transforms data from A to B. Both tables contain a column called x. The Glue job performs a GroupBy operation on this column x, which results in transforming all other columns from table A into list type columns for table B. I activate the bookmarking mechanism for the Glue job, so that it processes only new data. That requires, that I also read in inputs from table B (which are outputs of the previous run of the Glue job) in this job and append new items to the list type columns in case a record with a specific value for column x already exists. It is unclear for me how I could update the table B when saving outputs of the Glue job and avoid duplicated values of column x. Does anybody have a hint here? Thanks!