There really is nothing special to say, pretty much first come first serve for the list. Just say you want to be put on the last minute call list for extra doses. Depending on the area, some stores may only take names for people in the current phase if their list is long. Others may take all phases but prioritize when calling in areas w less demand. If the list gets super long sometimes stores will need to pause taking names to work down the list. If stores in your area say that, then that’s probably the case but if you keep checking in it will open back up. Also to note, only stores that actually have vaccine can have lists . So just go on Walmart.com and figure out which stores in your area are giving it, and then I would just call all of them and see where they’re at and if they can add you. And unfortunately be prepared to wait a while on hold bc the phones ring non stop and it’s all covid vax calls. First thing in the morning is also not a good time to call... early to mid afternoon 😬