@alijambo73 M666 is currently only for endstop adjustment on delta machines, though it has been added to the firmware wishlist, I think. Marlin firmware, and maybe others, allows endstop adjustment with M666 on other kinematics.
The work around is to either have an adjustable endstop on one of your Y motors (or both), or to split the Y axis motors into two separate axes, home them at the same time, apply a correcting move to one axis, then set a new axis position. Finally, recombine the axes into one Y axis. Your Y is defined as using drivers 1 and 3, and you have already defined one of them as U (though you don't specify M92, M566, M203 or M201 values for U or V, which you should), so your Y homing would look something like:
; homey.g
M584 Y1 U3 P4 ; split Y axis into Y and U
G1 H1 Y-1300 U-1300 F1000 ; home Y and U
G1 H2 U2 ; adjust U axis (could be Y axis you adjust)
G92 U0 ; set U axis position to 0 (this may not be necessary)
M584 Y1:3 P3 ; combine Y and U back into Y axis
G92 Y0 ; set Y axis position to 0
Well, I think that should work! For a full guide, see the 'Axis levelling using endstops' section here:
https://docs.duet3d.com/User_manual/Connecting_hardware/Z_probe_auto_levelling#axis-levelling-using-endstops
BUT look at the RepRapFirmware 2.x instructions, which split the axis as above. Also note that G1 S1/S2 commands from that guide should be G1 H1/H2 in RepRapFirmware 3.
Ian
