[Seisunix] Zero Offset VSP Processing

Hello Everyone I said before that I was trying to do Zero Offset VSP Processing. To do that, I tried to use free software is called MVSP and Crewes toolbox. My problem is that I can start picking first break arrivals from 4th trace, and I can not see and pick the first three traces when I look at the data during the picking. The first software itself assigns negative values for the first three traces, which results in negative velocities. On the Crewes, I am trying to assign values like 0.001 0.002 0.003 before the 4th trace because the 4th trace's time is 0.006, which probably gives rise to wrong velocities. In short, Can I do anything about this issue on Seismic Unix? Is there any chance to fix it? I added one of my files and the screenshot zoomed where the problem is. I modeled and created this data on different code (fdelmodc). **The data is passive data, and I utilized the noises, recording 120s. So, when you look at my data, you need to zoom in to see closely. Thank you Best regards Erdi