If you are taking in a date as an input field, you can use the calculator step to perform date math on it. If you are trying to grab the date from another row, then you can use the Analysis Step to get 1 row ahead to pull that date forward.
I usually end up using a Javascript Step and copy paste a good date math library into it as a 'startup script' and then create another tab in the step as the transform script and perform the calculations.
moment.js is helpful.