is expected to reach magnitude 11.8 on the night of March 6-7.
This is near the limit of a 4-inch scope; actual visibility depends on your observing site, your eyes, and the magnification.
You can get a more definite answer by trying to see stars of similar magnitude.
The other hard part is to acquire the target.
It will look like a star, so you need a finder chart showing stars at least as faint as the asteroid.
If you haven't observed one before, try finding a
around magnitude 10 first.
In this close approach, 2017 VR12 will move 0.9 degree per hour north-south,
fast enough that you need either quarter-hour marks plotted on the finder chart or a continuously updated display.
works pretty well for me; I downloaded some of the extra star catalogs, and I import the latest available orbital elements for the asteroid of interest.
If you wish to use your scope's go-to capability,
may help, but you still have to figure out which "star" in the eyepiece field is the asteroid.
identifies a few brighter stars you can try to watch it pass.
I do recommend getting a ~10mm eyepiece in addition to the 25mm one you have.
It might help you see stars half a magnitude fainter, but the main benefit is higher magnification for planets.