X-Axis Gantry Alignment

Hello guys, i got problem with my X-Axis Gantry Alignment The instruction says that the gaps must be as closed or equal as possible, from what I understand. My issue is that my left side (looking at the printer from the front) is closer than the right by approximately 1mm. I've tried adjusting the bolt tension screws, but it didn't help much. I think the frame isn't square, and I'm interested in the least complicated way to correct the frame to be square in this position. Thank you for your response, and have a pleasant day.