hi
I will assume that the driver motor on this machine is on the right hand side
on the left side it is an idler belt
problem: the grub screws on the idler side drive shaft ( left) are loose
make sure they are loose manually move the trammel and set it square with a reasonable quality square, tighten the grub screws, reset the mirrors and you should be good to go
been there got the T shirt
regards
Dave