Using manually created AWS DMS Replication instance with terraform code

I am new to terraform, I am trying to create AWS DMS resources with Terraform
first challenge was that I have AWS DMS Replication Instance that is manually created and I need to use it for creating new AWS DMS tasks.
I have seen that data source is not supported for this resource so I tried importing it and succeeded but when I run terraform plan it fails on ARN of AWS DMS replication instance
means that I cant use it in my AWS DMS file since aws dms replication instance not created by terraform
bottom line my question is how can I use existing aws resources with new terraform code
if it is by import what are the steps to do it?