At first you fall, and then you learn how don't fall.
At first you fall, and then you learn how not to fall.
At first you fall, and then you learn how to not fall.
auxiliary verb – also called "helping verb" or "linking verb". See Auxiliary Verbs.
how – is added to express manner or method of doing the action expressed by the infinitive. See Interrogative Pronouns.
infinitive – a "plain form" verb form that often appears with to. A structure with an infinitive is called a nonfinite infinitive clause (not "phrase").
infinitival nonfinite clause has a plain form (base) verb that usually occurs with to, which is analyzed as a subordinator, not part of the nonfinite clause. Similarly, for is analyzed as a subordinator of the subject of the infinitive clause. See Non-finite Infinitivals.
learn (V) – study or acquire knowledge: He learns quickly (Adv); He learned English (N); He learned that English was hard (that-clause); He learned to speak English (Inf Cls).
"Ice Skating." By Charles Rondeau, n.d., publicdomainpictures.net/en/view-image.php?. CC0. Accessed 2 Feb. 2020.