Never attempt to fit a soundpost yourself, even if you are a handy person. It is difficult and very precise work. Special tools and high skills are needed. Guus van den Braak has met numerous "experts" with plenty of "experience" doing more harm than good by moving or fitting a soundpost. These "experts" reposition the soundpost by hitting the soundpost in all directions with full string tension on the instrument.
The soundpost and especially the wood grain on the inside of the top and back are damaged with scratches and dents with this poor practice. This should never be done as it is impossible to feel how tight the soundpost stands between the top and back, and whether it fits properly. Fitting a new soundpost to the contour of internal dents is much more difficult and time consuming.
A soundpost should always be fitted or moved without string tension. Great care should also be taken not to damage the sharp edges of the f-holes. A soundpost will never fall over or move out of position if sufficient string tension is maintained. When strings need to be replaced, therefore fit one string at a time.