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"