Qunut means supplication. A learner who does not yet know the full Qunut may use one of the substitutes explicitly given by the source:
• اللَّهُمَّ اغْفِرْ لِي — 3 times; or
• رَبَّنَا آتِنَا فِي الدُّنْيَا حَسَنَةً وَفِي الْآخِرَةِ حَسَنَةً وَقِنَا عَذَابَ النَّارِ; or
• يَا رَبِّ — 3 times.
This gives a practical beginner path without pretending that a person must abandon Witr until the longer supplication is memorized.