Not exactly what you said but, maybe this
1. https://www.mangago.me/read-manga/secret_note/
And these are a few of my personal favorite omegaverse.
1. https://www.mangago.me/read-manga/a_tough_alpha_wants_to_be_loved_cornered_by_a_young_omega/
2. https://www.mangago.me/read-manga/unmei_no_kisu_wa_oazuke/
3. https://www.mangago.me/read-manga/koishite_baby_miyako_mimeko/
4. https://www.mangago.me/read-manga/youchina_koi_o_dou_shiyou/
5. https://www.mangago.me/read-manga/kasegimasen_kara/
6. https://www.mangago.me/read-manga/omega_wa_pink_no_yume_wo_miru/
!! Thank you! (づ￣ ³￣)づ
Any novel/manga where MC used to be omega but becomes Alpha and ends up with omega??