is a french first group verb. So it follow the regular conjugation pattern of the first group like: aimer
Follow this link to see all the endings of the conjugation of the first group verbs : conjugation rules and endings for the first group verbs
However, although the terminations are perfectly regular, stem can be irregular and have numerous variations.
Niveler is conjugated the same way that verbs that end in : -eler
Except a few verbs like verb modeler, verbs in -eler
add an extra « l »
or « t »
to the stem.