Easy! Assuming you want to put each string that you have split on a separate row, then you just need a loop:
foreach (string s in str1)
using (SqlCommand cmd = new SqlCommand("INSERT INTO myTable (myColumnName) VALUES (@STR)", con))
You could do this with the SqlCommand outside the loop, and it would be a lot more efficient, but that is an exercise for the reader - this just shows the general principle.
BTW: you don't need to call ToString on objects you already know are strings: it doesn't do anything useful and just looks like you don't care...