Setting up an n-gram analyzer

hi

im wanting to include a bigram option within my index for searching on...

i realise i need to add this at the point of indexing but am not sure how... heres my existing index create

clientTEST.CreateIndex(c => c
.Index("testcontent")
.InitializeUsing(indexSettings)
.AddMapping(m => m
.MapFromAttributes()
.IndexAnalyzer("english")
.SearchAnalyzer("english"))
);

do i create another .AddMapping area and how do i create the analyzer and analysis section . ive found examples using JSON but not sure how to translate into the NEST syntax...

This stackoverflow question seems to translate it to the NEST syntax