Plauti Assign is released in two phases - first a sandbox release, then a production release one or two weeks later.

If you are on Plauti Assign version 11.20 or up, both minor and patch releases are pushed automatically. There is no action required to receive these releases. 
If you disabled auto-updates, or if you are still on a version earlier than 11.20, you can download the latest version from the AppExchange website soon after the production release date; usually it is published there a few days later.

Please note that the dates listed below might be subject to change.