This is not as simple as it sounds.
The insertion point is set from the Start point on the Top Workplane which is usually a fixed point.
There are a couple of ways which may achieve this in an existing part and it really depends on how it's constructed or where elements are dimensioned from.
Before you do anything save a copy of the part using the built in tools, sometimes doing this we break the park leading to it becoming unusable.
You could create a dummy line in the direction you want from the Fixed point with a dimension to control the end location, as this is both an X and Y adjustment you may need a vertical line & dim as well as a horizontal.
You then need to find the constraint linking the geometry in the upper Top plane to the Fixed point, delete and reset the constraint to your new point location. This may cause things to go bad.
It may be simpler if you're confident enough to rebuild the model based on dimensions to control the vertical and horizontal location. You don't need to delete all the geometry but may need to rebuild some to suit the new location then amend \ rebuild the constraints to suit the amended locations.
In reality amending models can be more difficult than rebuilding them from scratch but that is an advanced workflow which needs a fair old learning curve.
Mike
Mike Evans
Civil3D 2022 English
Windows 7 Professional 64-bit
Intel(R) Core(TM) i7-3820 CPU @ 3.60GHz (8 CPUs), ~4.0GHz With 32768MB RAM, AMD FirePro V4900, Dedicated Memory: 984 MB, Shared Memory: 814 MB