How can one overcome the problem of involuntary nocturnal masturbation that leads to missing Fajr prayer, especially with commitment to fasting and unsuccessful attempts to prevent it?

The ruling on masturbation is that it is forbidden (haram). The questioner must fear Allah and seek His help, and strive against his soul to stay away from it by every possible means. If he expends all that he can, then Allah does not burden a soul beyond its capacity.