Here’s how to create a in Excel, since 12 is not a power of 2 (unlike 8 or 16).
In Excel (Columns A–E for clarity):
(1) Bye (8) vs (9) (4) vs (13) — but since you have 12 teams, adjust to: 1 vs bye, 8 vs 9, 5 vs 12, 4 vs bye, 3 vs bye, 6 vs 11, 7 vs 10, 2 vs bye.