On the www.iowadot.gov website, obtain an appointment to test for your permit at the Iowa DOT.
For Class A, you must pass three tests 80% or higher (General Knowledge, Air Brakes and Combination tests). Class B would take two tests (General Knowledge and Airbrakes). You will receive a paper copy. Keep this copy, never discard the paper CLP.
Note: Iowa CLPs are valid for one year from date of issuance.