You need to have the monitor repaired. It is a failing component in
the horizontal circuit. To adjust you need the custom interface jig
and software that the Viewsonic servicers have but no one else.

They will not be just making an adjustment if they fix it right.

Why would you be without a computer for weeks / months?
Computer monitors are cheap.
Pick up a good used 15" for $20 or 17" for $40, typical used prices. I
still have a spare 15" monitor in the closet that I use occasionally on
an old 486 based machine and will keep it as a spare should my main
monitor go down.