strapi/packages/strapi-plugin-content-manager/config/layout.js

module.exports = ({
  user: {
    firstname: {
      className: 'col-md-6'
    },
    lastname: {
      className: 'col-md-6'
    },
    about: {
      className: 'col-md-12'
    },
    createdAt: {
      className: 'col-md-6'
    },
    status: {
      className: 'col-md-6'
    }
  }
});