The first two steps are self-explanatory. The query is just querying the same record set for 0 records, but I also put all the additional data onto the schema that came off the schema when I first loaded it. I think this is so the new List has the exact same structure as the old list. Make sure you put the targeting dimension on there too.
Then I just save the new list as the same name as the old list
Hi @Ritu21 - the answer that @wodnicki gave is definitely one way to do it. I found another easy way to do it - just query the List for 0 records then save the List again. It preserves the List schema and purges the list by saving 0 records to it. The query just asks for records where the primary key is empty and the Update List just has the Purge List checkbox ticked.