The required field setting allows you to mandate fields. You can then mandate the microchip fields to accomplish your goal. I've linked a couple of guides below to help:
https://userguide.rescuegroups.org/display/WSG/Setting+required+animal+fields
https://rescuegroups.org/manage/animals_settings_fields_required
I want to require a Microchip number for all my animals. How can I make this required?