If you are going to migrate your current CMS to Drupal CMS and you also want to preserve your SEO links, then we recommend you to install Redirect module on your new Drupal website beforehand. (If you use other redirection modules, please, contact us.). In this way, the links of your Existing CMS will redirect to the New one.
Please install ‘Redirect’ module
After having installed this plugin on your newly baked Drupal website, choose “301 Redirects from old URLs to new URLs” option in your Migration Wizard and go on with your migration.