r – How to prepare data and perform a sensitivity analysis?

I have a dataset with one dependent variable and three explanatory variables that I plan to correlate through a lm or glm. I also want to determine the influence of each of those explanatory variables to the overall dependent variable through a sensitivity analysis. How can I perform it with a basic R script? How do I decide values that it requires, such as weights? Maybe are there simpler alternatives?

I tried to apply the scripts from several examples I’ve checked in the internet, but in general, their datasets are more complex than my case: they have different treatments or they has to build an ASEM object, which I barely understand what it means. So I don’t know exactly what should I include in each section of the sensitivity analysis.

Thank you.