How to prepare yourself for a master's degree in pm-a?

Question

IT education

In the bachelor's degree there was a different specialty, we were something like an experiment ("recipients of the specialty applied mathematics", as we were called). In general, the trouble is, they gave the subjects in the wrong order, for example, the theory of optimal control, which is tied to difurs, we were given up to the difurs themselves ... There are many examples, one way or another I want to systematize my knowledge so that I would not be expelled from the master's program of another university.
A question for people who graduated from a university with a degree in applied mathematics and computer science, which subjects are better to pull up? I ask the question here, because most of the PMs are it-shniks.
Forgive me if I'm asking something stupid or in the wrong place, but thanks in advance for the helpful answers.