First, call the Ohio dept. of Ag and request the study materials for category #8. Then, study hard until you know it. 8 is not too hard to pass. I am now studying for horticulture. (vegetation control is included in the hort. category, not lawn). It's tough!!!
Then, you will be given a list of locations and dates as to where to take the test. When you pass, you will need to buy pesticide liability insurance. Then a pest business licence ($100) and pay for your first year ($30).
Hopefully you have assessed equipment costs and have located a product dealer near you. (if not, shipping can be expensive)
Finally. you need customers. I wish this part was as easy as the above.