In the batch settings, there is an option to select the file save type. If the jpg option can’t be selected then it is because you selected the option to run a batch for “cutout” images. With cutout images, jpg is not an option because the jpg file format doesn’t support transparency. So it the images are cutout then you must save as TIF, PSD, or PNG. There are several batch settings that give different option based on whether you select the option to run the batch for cutouts or non-cutouts.
Assuming the images are not cutout, and JPG isn’t an option then you need to first go back to the Home Menu in face Crop. You will see a button on the bottom that says Home Menu. Click on that. The clickthe button that says “Batch For Non-Cutouts”. The you will be able to select JPG as the save format.