I just found that by using a specific map tool in Wolfpack would make the plotting of 4-bearing method much easier, and also less error prone (i.e. you don't need that triangle formed by the 3 bearing line anymore).
Let's say you have taken 3 bearings while moving, as shown in the video for illustration purpose. And the core methodology behind the 4-bearing method is to find the imaginary 4th bearing line (also called the Spiess Line).
In Wolfpack, there's a handy map tool function called 'draw from midpoint', which can help you find a line splitted equally by the 3 bearing lines. By randomly picking two points on the 2nd bearing line as a starting point, you can extend the lines with equal length to define the Spiess Line.