Control Panel > Content Rebuilder > Transition Actions

The UTF8mb4 Transitioning Tool is located within the bottom section, just under the HTTP to HTTPS Transition Tool.

Quote
Update All Tables to UTF8mb4
Update database table collations to 4-Byte UTF-8 unicode language encoding (eg. utf8mb4_general_ci). 4-Byte UTF-8 Support requires MySQL 5.5.3 or above. Depending on the size of your forum and tables, this process may take a long time to complete.
Note: It is highly recommend to create a database backup as this process cannot be undone.


Current developer of UBB.threads PHP Forum Software
Current Release: UBBT 7.7.5 // Work In Progress: soon
isaac @ id242.com // my forum @ CelicaHobby.com