You can use this bash script to convert all tables in the database.
Make a backup first!
#!/bin/bash DB="go61mb4" COLLATE="utf8mb4_unicode_ci" USER="root" PASSWORD="SECRET" ( echo 'set foreign_key_checks=0;ALTER DATABASE `'"$DB"'` \ CHARACTER SET utf8mb4 COLLATE '"$COLLATE"';' mysql -u "$USER" -p"$PASSWORD" "$DB" -e "SHOW TABLES" --batch --skip-column-names \ | xargs -I{} echo 'ALTER TABLE `'{}'` \ CONVERT TO CHARACTER SET utf8mb4 COLLATE '"$COLLATE"';' ) \ | mysql -u "$USER" -p"$PASSWORD" "$DB"