Tor: How do I connect when Tor is blocked?

Short answer

Open Tor Browser's connection configuration and try Connection Assist or an available bridge or transport. If one bridge has stopped working, request a fresh one through a Tor Project method and enter its full address. Also check that your device clock and ordinary internet connection work; a failed connection is not always censorship. The Tor Project's troubleshooting guide explains how to inspect logs.

Sources

Tor Project: Using bridges, Tor Project: Troubleshooting.