Ighalo, 31, was part of the Watford team that were defeated 2-1 by Crystal Palace in the semi-final in 2016, a result that denied them the opportunity to face United in the final.
"It was a difficult one to take against Palace. If we'd have won, we'd have played United in the final," the Nigerian striker told the United website.
"Unfortunately, we lost. It was a bitter one to take but this is an opportunity to make it right and go forward to the final... To get to the final would be great for me in my life and my career. It would make my dreams perfect."
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Ighalo, who extended his loan deal at the Premier League club from Shanghai Shenhua until the end of January 2021, has scored five goals in 15 appearances in all competitions.
However, with strikers Marcus Rashford, Mason Greenwood and Anthony Martial in a rich vein of form, Ighalo has found himself consigned to the substitutes' bench.
"They are doing so well. Seeing them playing every week is a joy. Rashford has come back from his injury and is doing well. Martial is scoring goals, Greenwood is unbelievable, he is such a good finisher with both feet," he said.
"The team is doing well and the three forwards are scoring goals and that's what we need - goals win games."