You have a couple of options. The best involves creating a JSON file of the visualizations. The transfer between Kibana UIs involves a saved JSON object of all index patterns, visualizations, dashboards, etc. You can go to your saved objects in your new environment, reduce it to just visualizations, and then export all of the saved visualization objects to a JSON file. Next, you will need to know the _id of the old index pattern and the _id of the new index pattern. You can find these usually in the .kibana* index pattern (just add it as a pattern) and look through the index ids in the Discover tab (or build a Kibana table of the same). Once you have this, just open that visualizations JSON in something like Notepad++ and do a find and replace. When done updating the objects in bulk, import that visualization JSON file back in to the environment and overwrite what was there. You may have to make a few changes here and there (I always forget something when I do this) but it should work.
Your other option is to do it all manually, one by one. I don't recommend this...still haunts me to this day (updated 800+ visualizations and saved searches manually once).
Hope that answers your question!