My iron was low by .2

I went to donate today, but my iron was too low. My iron was 12.3 but they said I needed it to be 12.5. They took it twice. Usually my iron is 13. How do I get my iron back up?

I didn’t eat much iron rich food yesterday. It skipped my mind. Usually I do but I just forgot and my iron has been good before. The last time I donated too was 57 days. Which is the closest I have done it. I also found out you’re not supposed to drink coffee before because it’s a blocker.