1. The best way is to roll-back the backup.
2. If you didn't create restore point, try disabling Mageplaza extensions by module:disable command. With normal setup, the command will look something like this: php bin/magento module:disable <extension_name> where you can get <extension_name> by running php bin/magento module:status
3. Before sending a ticket, please make sure you followed all the steps we described in our installation guide: https://www.mageplaza.com/install-magento-2-extension/
4. When sending us a ticket, please describe the issue in as much detail as possible, including screenshots. Zip the var/log folder, upload to online storage services such as drive, Dropbox and share it with us if possible.