How to build small learning drips

Hi,

I'm looking for idea's on how to create and distribute small learning drips.

We drive a large online trainingsprogram (4500 users) in which we train a lot of product knowledge. 80% of the target audience has taken the online courses but now the product is changing in a rapid speed. We do not want the learners who already followed the online course to do them over again with the new content but want to train them via small online learnings which train the additions and/or changes in the product. 

I'm very curious on what the thoughts are on this challenge

Juri