Again, no syntactic sugar here. Instead you’ve got to look at the functions for the logistic distribution. In particular, the logit transform, $\mathrm{logit}(x) = \log(\frac{x}{1-x})$, is given in R by: qlogis(x). The inverse logit transform, $\mathrm{invlogit}(x) = \frac{1}{1 + \exp(-x)}$, is given in R by: plogis(x). Check that the inverses are good: for example, plogis(qlogis(0.6)) and qlogis(plogis(0.6)) should both give 0.6.