Select the reverse primer you just extracted. Go to Primers→Add 5' Extension.
Select Extension Type: Restriction Enzyme, Enzyme Set: Commonly Used, Enzyme NcoI and click OK
Now you have the extension added to the primer, turn on Complement in the sequence view options and note how many bases are introduced between the primer binding site and the cut site on the reverse strand (1).
The two bases which are introduced at each end of the PCR product are going to cause a frameshift and destroy our protein because they are not a multiple of 3.
To rectify this, turn on Allow Editing and insert another G (C on the complement) just between the NcoI recognition sequence and the primer binding site. Do not put it in the region annotated as primer as this will cause the primer annotation to disappear. Click Save and our primers are ready to be ordered.
Select Human Proinsulin again and delete the two primer annotations.
Test the new primers by going to Primer→Test with Saved Primers. Choose your forward and reverse, turn off the Included Region, Target Region and Product Size options if they are on, and click OK.
Hover your mouse over the reverse primer annotation and note the "Extension" which we added - note that the second NcoI restriction site won't show because it is on the extension but it is there so don't worry.
Now use Primers→Extract PCR Product to pull out the PCR product. You don't need to select forward and reverse primers because there are only two. Note that the result will now have NcoI sites on both ends.