Not_analyzed string field - case-insensitive search


i have a problem searching on "not_analyzed" string field, with case-insensitive search.
i saw that there are solutions such as multi field, but me problem, is that i have many TB of data, and i'm not sure i can reindex all the data.

the cause of this problem, is that i have data coming from another database with lowercase values, which i need to search in elasticsearch.

for example: i get the word "desktop", and the value in elasticsearch is "Desktop" (i can not know the values format in ES before the search, cause there are tons of values)

is there anything i can do to filter with case-insensitive option? Such as adding some query string to the _search request..?

eventually i found this syntax which works(not sure of its performance or other issues with it)

GET index/type/_search?query=device:desktop