Yes, you understand it correctly.
The endorsement exams are given at the location of and during the same time of the CWI exams. Just look them up and you will know when and where they are available.
You need to pre-register for them just like for the CWI exam. Some have seminars available but most are NOT available through AWS.
You will NORMALLY be in the first testing group on Sat morn and be on your way as soon as you are finished so it pays to do it as close to home as possible to keep expenses and time requirements down.
Have a Great Day, Brent