how to use /haʊ tə ˈjuːz/. After how to, the verb keeps its base form, so how to used is not standard.
used to /ˈjuːstə/ plus a base verb shows a past habit or state no longer true: I used to live here. It is the fixed past form of 'use to' in statements; the written -d devoices after /s/, so /d/ becomes /t/ and you hear /st/ before 'to'.
After did, standard writing drops the -d: Did you ____ to live here? takes use, because did already marks the past and the -d would double it. In a plain statement the opposite applies and this statement form keeps the -d: I used to live here.
After did: use to
After did, the standard form drops the -d: I didn't use to like coffee. Since did already carries the past, adding -d again is redundant in standard grammar.
Same rule in questions: Did you use to live here? The question word did does the past-tense work, so the verb stays as bare use /juːz/.
A spelling trap hides in the sounds: verb use is /juːz/ with voiced /z/, while noun use is /juːs/. The -ed in used to is pronounced /st/, /ˈjuːstə/, which is why the written -d often goes missing after did.
One restriction: this only covers negatives and questions with did. In a plain statement the -d stays, because nothing else in the sentence marks the past: I used to like coffee. I used to live here. Note that would does not take the -d form at all, so I wouldn't used to swim is never standard.