Is it possible to create AWS RDS as replication from external server? I can't find any tutorial to create a new instance of AWS RDS (MySQL) to be an replication db from an external db server. Is it possible to create one?

Thanks.
yes , you can,
check below link.
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/mysql_rds_set_external_master.html