how do I enter in my estimated mash efficiency?

The est mash eff field is set to 82.9% and the field is not editable.  How do I go about changing that?  I do BIAB and used the BIAB equipment and mash profiles to make my own

the estimated mash efficiency is not editable..it is a calculation by the program itself based off measurements you can take and plug in during brew day (such as pre-boil gravity, post-boil gravity, etc), and based off the numbers given it gives the estimation of what your efficiency should be. you can change your efficiency itself (measured, or what you know your system's efficiency is) by clicking on your recipe as if you were editing the recipe (adding/removing ingredients screen) and simply clicking on the number in the "Tot efficiency" field up top..

The mash efficiency is essentially calculated back from the brewhouse efficiency.  BeerSmith uses brewhouse efficiency instead of mash efficiency to estimate gravities.  See this article for a further explanation:
  http://www.beersmith.com/blog/2008/10/26/brewhouse-efficiency-for-all-grain-beer-brewing/

Cheers,
Brad

Thanks, I adjusted my equipment profile, so I'm in the ballpark of my reality.  Now if I can figure out how to eliminate the sparge step, I'll be cooking with gas

Just as a heads up, I would worry more about getting it to predict the SG than getting it to agree on your mash efficiency.
I need my mash efficiency in BeerSmith 2 to be about 6% over what it comes out to be on paper to have all my measurements within reason and have it predict the gravities correctly.
And if I add something like maltodextrine to the pot the BeerSmith mash efficiency goes nuts.

I just completed my first brew with my new grain crusher.  My mash efficiency went from 58% to 89% with the crusher set to almost the most fine setting.  This naturally threw off all my volumes.  I re-read Dr. Smith's article and came up with the attached Excel sheet that I use to figure out my efficiencies. 

The numbers seem to work out really well based on my experience.  A great way to test your system is to get 1 lb of a base grain and make 1 gallon of unhopped wort with it using Beersmith software.  Take gravity and volume measurements pre and post boil and plug the numbers in to the attached spreadsheet.

Cheers.

;D

Keep in mind that you want to avoid grinding the grains and really want to crush open the grains exposing the insides leaving the hull intact.  You wand yo keep all the hulls in the mash as well as keep prevent the lautering from getting stuck.    Hulls in the boil result in tannins in the beer which are kind of puckering and drying on the palate.  OK in a red wine but not so much in your beer.