您需要使用globalsecondaryindexupdate方法来执行此操作，如下所述：https://docs.aws.amazon.com/amazondynamodb/latest/apireference/api_globalsecondaryindexupdate.html
应该是这样的

CreateGlobalSecondaryIndexAction action = CreateGlobalSecondaryIndexAction
                .builder()
                .indexName("index-name")
                .keySchema(theSchema)
                .build();
GlobalSecondaryIndexUpdate index = GlobalSecondaryIndexUpdate
                .builder()
                .create(action)
                .build();
UpdateTableRequest request = UpdateTableRequest
                .builder()
                .tableName("table-name")
                .globalSecondaryIndexUpdates(index)
                .build();
dynamoDbClient.updateTable(request);