Add another subject test for June

DD already registered to take Math II in June, but would like to add another subject test, what is the easiest way to add the test?
I tried to log onto SAT, it seems that it only allows to change test center/ test days or switch between the regular SAT and SAT subject test, but not an option to addanother subject test. I recalled reading old posts that student can just add the additional test on test day…should DD tell the person before going to the room or to the proctor after she finishes Math II? Does she need to bring money to pay ?

She just needs to stay for the 2nd hour. She can tell the proctor, but it really is not needed.

https://collegereadiness.collegeboard.org/sat-subject-tests/taking-the-test/test-day#changing-tests

thanks for posting that link. I specifically called college board this morning asking this same question. DD wanted to reschedule her May Math II exam for June. She is already registered for another subject test for June. I was told by College Board the soonest date she could reschedule the May 6 exam was August 26th. CB made no mention that she could take a second subject test during the June sitting. I asked multiple times during the call if she could take more than one subject test during the same day and was told no.