This wiki explains how to do a sensitivity analysis on GroIMP models using the GroR interface using a Morris screening over input parameters of the "Example08" FSPM model from the gallery as an example.

Make sure to set up GroR. Play a bit around with it and get a feel for how it works and what the different functions do and what they return. The approach presented in the wiki here is just one way you could approach a sensitivity analysis. You will likely find your own approach for your specific model, but GroR will be the space you work in.

source("path/to/GroR.R")
...