It's not in the plea agreement, but that phrase appears multiple times in the Information (the charges to which Cohen actually pleaded guilty). The Information is the second document on this page (right below the plea agreement. The "influence the election" phrase is in paragraphs 28, 30, 35, 42 and 44.
That’s what they used the word “allegations” about describing counts 7 and 8 in the second document.
A guilty plea is not an adjudication of a court even though the feral media and Davis are acting like it is.