S.H.
Its a viral rash.
AFTER a fever.... a baby/child can get a 'rash' like you described... both my kids have had that too. More than once. After a fever.
It is actually, the virus leaving the body.
This is per our Pediatrician... who examined my kids with it.
If you read about it online, it will not seem so nerve wracking.
It is not painful nor itchy... for the child. It is temporary.
No need to do anything to it.
It will go away.
all the best,
Susan