if you already have blasties on ice, they will thaw one at a time until they get one that has survived the thaw. hopefully, you'll have a good thaw, and the first will survive - though it's been known to take several embies being defrosted before a strong enough one is found

FWIW - i have had four embies (day 3) frozen, and all defrosted perfectly. another friend has had several frozen, and had bad results at thaw. it's unfortunately something no one can predict. even from one cycle to another for an individual, results will vary greatly...