Hi,
if you use TmoleX, just visualize the imaginary frequency, distort it a bit along the mode and generate a new job from those coordinates (the green big button on the lower right side of the viewer). That does the same job as screwer does.
Small negative (or imaginary) frequencies can also stem from numerical noise. If you ran a DFT job, try to increase your grid size from 'm3' to 'm4'.
Regards,
Uwe