In a previous article, we worked through implementing the Exchange DKIM Signer. Here is the article for reference:
I was running V3.3.4 at the time and checking my lab today, there is an update available which you can run from the Exchange DKIM Signer itself. Do take note that they have removed support for older versions and do caution you to update to V3.4.0.
As you can see below, the software shows what you have installed and what is available.
Just like many applications, you need to start moving to supported versions of Exchange, especially with the threats that are active in the wild. Un-patched software and Exchange servers are an open invitation to attack and Ransomware.
Hope it helps.