To cite ruODK in publications use (with the respective version number:

  Mayer, Florian Wendelin. (2020, Nov 19).  ruODK: An R Client for the
  ODK Central API (Version X.X.X).  Zenodo.
  https://doi.org/10.5281/zenodo.5559164

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {ruODK: Client for the ODK Central API},
    author = {Florian W. Mayer},
    note = {R package version X.X.X},
    year = {2020},
    url = {https://github.com/ropensci/ruODK},
  }