Create Index and Mappings

Hi all,
I am running elasticsearch dot net Version 7.1.0 and using elastic search 6.3.0. I want to know if index exist or not. If it exist then index data otherwise create the index with mappings but i am unable to do so. What i have done is as given below
var request = client.Indices.Exists<ElasticSearchRelated.ElasticSearchResponse>
("3YrsCustomerData");
it will check if index exist or not but how would i be able to create index as there is no api for that

this is only create and create async api.