Kevin - increasing the Cation Exchange Capacity (i.e. CEC which indicates the ability of the soil to hold nutrients) will help increase Potassium levels.  See the article below for more details on this topic.

https://www.canr.msu.edu/news/what_is_your_soil_cation_exchange_capacity

Increasing the organic matter in the soil is the key to raising the CEC.  More info about organic matter is in the article below.  Methods for increasing the organic matter would be to mow high and leave your grass clippings on the lawn (i.e. use a mulching blade), top dress with organic matter and/or mulch leaves in the fall.

https://www.canr.msu.edu/hrt/uploads/535/78622/Organic-Matters-figure-6pgs.pdf

I would recommend you wait 3 years before your next soil test since raising the organic matter and Potassium takes time.

I am also including a link below to the MSU Gardening in Michigan Lawn web page that has info I thought you may find interesting.

https://www.canr.msu.edu/home_gardening/lawns/

Hope that helps and good job using the soil test to know the health of your lawn!

I have a suggestion that worked for my lawn (when I too had low potassium, little organic matter and nothing that seemed to work).  Instead of applying Milorganite (which is a quick-releasing Nitrogen that most likely is largely  washing through the soil), I suggest you switch to using a Winterizer fertilizer which is slow releasing.  With a slower release, the fertilizer can be taken up slowly by the grass.  When I did that for a few years , added a Potassium fertilizer, and mulching, I was able to increase both the organic matter and potassium level in my soil.

Hope that helps