Generally, for 16S rRNA gene sequences, you do not need to... as the adapters are often before the primer at the 5' end. The only time you may need to worry about this is for very short marker genes were you "read-through" the 3' end in a single read. In which case, you can simply use the approach outlined here, where you'd simply add the reverse compliment of the opposite primer and/or adapter. Again, most do not need to do this for 16S rRNA gene sequences.