It's just a few lines on the first page of the 706, right?  You can find the fillable pdf for that here.  

https://www.irs.gov/pub/irs-pdf/f706.pdf

If you don't want to fill out the whole page, use correction tape or fluid.   If that looks messy, make a copy and type in the correct figures.  

Humans knew how to relieve themselves before indoor plumbing.  Tax preparers should know how forms were filled out before computer software.