Fighting varroa mites is often done with chemical pesticides. These drugs have an effect but also have a negative influence on the bees. Biological control is a better way and you can use predatory mites for this. The Stratiolaelaps scimitus is a natural enemy of the varroa mites and reduces the varroa mite population.
1 package with 5,000 predatory mites is sufficient for 1 hive.