Do not attempt this unless you are aware of the dangers, and know what you are doing. To attempt this repair, you'll have to remove the top cover of the Lisa's case, exposing you to possibly dangerous voltages. BE VERY CAREFUL not to touch anything. If at all possible, attempt to find plastic CRT adjustment tools. Work with one hand behind your back - this will prevent you from accidentally completing a high voltage circuit. Wear eye protection and be careful not to touch the CRT as it is very fragile and can implode if hit
Use the plastic adjustment tools to turn the R34 HOR PHASE potentiometer on the video board. Before adjusting any potentiometers, you should mark their exact positions using a felt tip marker. Note that these pots may have been previously sealed and may require some force to break the seal. If you're a dare devil with no regard for your own life, you could use a metal screw driver, but you're risking your own life.
If you feel uncomfortable with this adjustment, find someone who can do this for you, such as a technician at your local TV repair shop.
If the adjustment range is insufficient and the revision 3A ROMs for the square pixel screen modification kit are installed, the problem may be that the transformer that was included in the kit was not installed. This small cylindrical transformer is connected between the CRT yoke and the video board.[LisaFAQ] > [Hardware] > [Video and CRT] (Comment on this answer)