Just putting a value in the "Organism" field of the "Primer Pair Specificity
Checking Parameters" section is enough. Click the question marker followed
by each parameters to learn more, such as
"With this option on, the program will search the primers against the
selected database and determine whether a primer pair can generate a PCR
product on any targets in the database based on their matches to the targets
and their orientations. The program will return, if possible, only primer
pairs that do not generate a valid PCR product on unintended sequences and
are therefore specific to the intended template. Note that the specificity
is checked not only for the forward-reverse primer pair, but also for
forward-forward as well as reverse-reverse primer pairs."