Originally Posted by R.A.S.

Are you talking about "single pedal C", "double pedal C", or just "low C".
Please describe.

If it's the single pedal C, I've been playing for 25 years and still have trouble getting that note out with open fingering. I usually use 123.

If it's the double pedal C, it will come in time.

If it's just the C one line below the staff, consult with a good teacher! You may need help with the way you approach the whole range of the instrument. I am specifically referring to the kind of advice that is on the Monette site (in their acclimation guide). Very helpful information, and an issue many players struggle with. Someone like Manny Laureano would be able to assess the problem and help you solve the problem.