How to force the order of a b to be normal?

I have one auther with two publications in the same year. I am faceing a problem that it starts with b and then a

for example the first sentence is smith et al., 20013b

and then latter in the doceument it is smith et al., 20013a

logically smith et al., 20013a

should be before smith et al., 20013b


Logical is not how publishers view things.  They define the sort order, which is usually some combination of alphabetical authors, title. and care little if the “b” comes before the “a”.  You can refer to this threadto see if it helps and this one