Higher pre-boil efficiency

I'll be brewing a nut brown tomorrow and I'm calculating everything based on 60% efficiency, which is what I got last time. I also plan on adjusting for some mistakes and hope to get a higher eff. I'm still going to err on the side of caution, but if I do end up with say 70% efficiency bre-boil, how do I know how much water to add, and at what step do I add it (to the boil, or the carboy)? I'm looking through beersmith and not finding a spot to make that calculation. Thanks!

Use the dilution tool. Its located under tools.

Got it, thanks!