I have the same problem (e.g. oval holes instead of circle...) and am trying to find a solution as well right now (I would like to use this technology for engineering purposes).
There is an icon at the left side of the screen to scale the model. You can increase/decrease the scale in three directions: "x", "y" and "z".
According to my experiences, "z" dimension is correct (this is obvious since it has been defined by the elevation steps of the platform) so you can leave this rate at 100%.
At the same time, x and y rates are not 100%. I use Liqcreate Strong-X resin at the moment and the printed "x" and "y" dimensions are roughly 5% bigger than they have been designed originally in the 3D CAD model. This is why I try to compensate it by using 95% scale values in "x" and "y" cells instead of 100%.
I hope it will be okay.

However, the correct solution would be to print a reference cube I think (e.g. 30x30x30mm) and to measure the right distorsion rates in each direction.

(Sorry, I am not a native English speaker...)

Well, this is peculiar! If you chose an AnyCubic Photon printer... there is an option under Machine tab! Check the image below.