Hi @jhlee857,
Restoring from a backup is a one-time imperative operation and so not really a good fit for Terraform’s declarative model.
With a suitable provider design is is possible in principle to describe restoring a backup, but that then raises the question of what should happen once the backup has already been restored and so the configuration ought not to go on referring to the old snapshot forever.
Instead, folks typically handle this sort of exceptional situation by using the AWS CLI to request the restore and then import the resulting object into Terraform so that it can be managed there in the future.
This is a pragmatic answer for an action that is hopefully taken relatively infrequently. (Though be sure to rehearse it in a non-production environment so you know that your restore procedure will actually work!)