Now have to do it through Costco Travel website. They do give you
Alamo’s number to link it to your Alamo account, after you reserve with Costco Travel.
Only thing I found, was I had reserved a car with Costco code on Alamo before it could no longer be used, and I had to call Alamo to cancel. If I need to cancel my Costco Travel one, do it right on your Costco Travel account. And even though I had linked that cancelled reservation on Costco Travel, next time I checked my Alamo account it had disappeared, so obviously, Costco Travel does update Alamo quite quickly for cancellations.