If everything really is square in the machine, and it is just the router that is angled, then the problem is solved by shimming the router. There are no adjustment screws. You would need to insert shims in the mount until the router is at a right angle. You would use a tramming arm like this one to magnify the angle to help with the adjustment. Last time I check, there were several on Thingiverse or you can assemble one from a scrap of wood.
But before you use your tramming arm, you need to surface (cut off the top) your spoil board. Typically surfacing is done with a larger (25mm) bit, often marketed just for surfacing like this one. Tramming without surfacing is not a good idea. If your router is not at a right angle, the surfacing will leave ridges. That is okay. The ridges will be reduced or disappear once you do the tramming and then surface your spoil board again. Note that it is generally recommended to get some hours on your machine before surfacing the spoil board. Other problems may be found and solved in that time that might impact the surfacing.
While the above will do the job, if you are off significantly from a right angle, then I’d carefully check the assembly and the parts.