I seen (or he seen, she seen, you seen, they seen, or we seen) is substandard grammar. Do not use seen as the past tense of the verb to see. The past tense is saw, as in the old movie The Last Time I Saw Paris or the old song I Saw the Light. (The conjugation is I saw, you saw, he/she/it saw, we saw, you saw, they saw.)
Seen is the past participle of to see; it should be used with the auxiliary verb to have, as in My eyes have seen the glory… or He has seen the light. See?