Unfortunately, that does happen from time to time. You will need to log into your hosting and revert the site back to the last save point. If you are unsure about how to do that, feel free to call our favorite hosting company. WP Engine has an amazing 24/7 support service that is included in your hosting. 1-877-973-6446.
If you are tired of maintaining your own site, let's talk about moving you to a Care Plan so that future update issues become our problem rather than yours. You can learn more about our Care Plans here: https://hookedoncode.com/care-plans/ or schedule a call to discuss how we can take care of your website needs here: https://calendly.com/hookedoncode/30min