>how long it'd take for my iron levels to get good by simply eating a steak once a week
Probably never.

Six to twelve months by diet alone if you eat a proper diet.
Three to six months with proper diet and supplementation.

But, get this, I'm not your doctor and this isn't a prognosis or diagnosis. I don't know your haemoglobin or your ferritin levels, I don't know the cause of your too low to donate blood iron, I don't know your body mass, the size of your meals, the range of foods you eat, what foods you eat with other foods, your general health, your history of iron level let alone the rest of your relevant medical history. There's just no way you can ask randos on the Internet how long it's going to take to to get better from an unknown degree of badness by doing one thing to an unknown degree that might provide a little remedy but might not. You need to see a doctor if you want actual answers not wild estimates based on too many unknown factors.

>>1567788
Hey OP. Frequent blood donor here.

I just want ot reinterate what >>1568109 says. Go to a doctor first and tell them what the blood collection told you. While iron deficiency is not the end of the world and might be a problem in itself, it could also be a symptom of a larger problem.

Iron levels fluctuate in relation to diet and general health; that single piece of meat is not good enough to make a difference in a week. Dr. Google - a guy I trust as much as any rando - will suggest eating iron-rich foods like vegetables, and not just meat, to increase and maintain your iron levels, be it for blood donation or just not feeling like shit throughout the day.

I have donated blood for more than a decade and the only time I could not donate blood due to low iron was because I was also developing an ulcer, whose own symptom should have been a hint that something was wrong, but hey, I didn't have medical insurance to do anything about it. It got worse and I eventually got it fixed but that is another story.

I have also taken iron supplements. I have taken them daily for years and I think it works. If you are in the US, the Red Cross Blood Donating app allows you to track your iron levels for years and mine has been consistently high, except for that one time several years ago when it dropped like a rock.

With that in mind (and I am not a doctor!), I would say give yourself a month or two to get your iron level higher and the opportunity to stay there. Go to a doctor, make some changes to your diet, and perhaps use iron supplements.