To cite hmmr in publications use:

  Ingmar Visser, Maarten Speekenbrink (2021). Mixture and Hidden Markov
  Models with R. Springer.

A BibTeX entry for LaTeX users is

  @Book{,
    title = {Mixture and Hidden Markov Models with R},
    author = {Ingmar Visser and Maarten Speekenbrink},
    year = {2021},
    publisher = {Springer},
  }