At the moment Filters/Rules feature is not currently supported in Mailbird. It is planned for development and will be available in the one of upcoming major Mailbird releases.
For now, if you are using IMAP in Mailbird, most email provider usually provided filters/rules from their webmail. Setting your filters this way is much more convenient and powerful than setting it up in an email client. Because not only that the filter will run 24/7, you only need to set it up once for all your email clients in all you devices, including mobile ones.