Tilt the enlarger head one way and the easel the other. Tilt the lens towards the projected intersection in space of the first two. Done with precision, you will be in focus top to bottom.
Add a rulled grid to the easel to set up the parallel lines and remove it when you add the photopaper.
The top of the image gets stretched in width to match the bottom so you no longer have converging parallels. It is a different correction than in camera as the image is stretched lengthwise some.
More exposure is needed in the wide stretched top than the bottom. Figure the difference and do a base exposure for the narrow part and then a slow burn top to bottom to get the extra exposure for the top of the pic.
Phillips PCS130 enlarger has all the controls to do this perfectly. It is a total pain without the proper enlarger controls. This is mostly why I bought the machine.