Computing Aliases while creating the Index Template in Elastic Search 8.x

Question

I have created the index template in elastic search 8.5.3. Here, I need the alias creation with a dynamic name.

For example, if the index name is, es.contact100 then the alias should be as.contact100.model.

I used this one,

{ "as-{index}": {} }

But, the output is, as-es.contact100

Please help me to resolve this.