how i supplement list linq sql?

i have list database i'm retrieving controlling linq sql, biased guess i wish supplement list, following transform database new equipment + any changes i've made.

what i guess i this:

var list = (from vigilant db.table
            name item).tolist();

[do guess where i cgange equipment & supplement list]

list = list.distinct();

db.submitchanges();

what happens modifications happed (ie. sql updates) nonetheless any new equipment i supplement list don't added.

obviously i'm doing wrong, repremand proceed cgange & supplement list db entities, following dedicate updates & inserts?