Divide the DyanamoDb tables into N Segments logically, and distribute those segments among worker process/threads. Each worker process will read at max 1MB of data in each read request then request for next 1MB using the LastEvaluatedKey.
Medium Blog: Reading Millions of DynamoDB Records in Distributed Parallel Batches
Processing same table in parallel and different table sequentially.
Write or update data enabling retry mechanism.