Retraining FSRS
FSRS uses your review history to predict when you are likely to forget a card. As you complete more reviews (training data), retraining updates the FSRS parameters to better match your personal memory patterns.
To retrain FSRS, open Deck Options > FSRS > Optimize. Anki stores deck settings in presets, which are groups of shared options that can be assigned to one or more decks.
Optimize Current Preset retrains only the preset currently selected in Deck Options (Ex: Default, or Anking). Optimize All Presets retrains every preset in your collection. If you only use the one preset, both options will produce identical results.
Retraining about once per month is a reasonable, and forgetting is not the end of the world! FSRS remains effective even if you go several months without retraining, it might just not the most perfect version of itself for your unique review style!