I started weaving on this Summer and Winter warp and only after messing about with the cloth advance for a while, cutting off, re-sleying and started weaving again did I realize that I’d had a brain cramp while threading and that 3 units were threaded onto the incorrect shaft.
When you have a threading error there are several different ways of fixing it.
In some cases the only way to fix a threading error is to cut off, remove the warp ends from the reed and heddle and re-thread from the error onwards.
In this instance since everything else is correct and the error is that the pattern ends are on the incorrect shaft, you can either cut the offending ends, tie in a repair heddle, thread the ends correctly and then deal with the cut ends, re-attaching them to the rest of the cloth.
OR, you can do as I do in this instance and tie a repair heddle so that the incorrect end is contained within the eye of the repair heddle and then cut out the incorrect heddle.

I begin by identifying the incorrect ends by marking them with a coloured thread. By lifting the ends up, you can then mark the ends behind the reed like this:
Having a visual marker of where the incorrect ends are located means I don’t have to go hunting for them as each one is corrected – in this case, 6 warps.
I generally have lots of 2/8 cotton around so I use a doubled length a different colour than my heddles or warp to make it easy to see what I’m doing. Here I’ve looped the repair thread around the bottom of the shaft and tied a double knot at the same level as the bottom of the heddle eye and passed one side of the repair thread so that I can now tie the eye with the warp end travelling through the eye. Like this:
New heddle eye tied with the warp thread passing through it.
Repair heddle tied on shaft three with the warp end now passing through the heddle on shaft four and three.
The incorrect heddle is then carefully cut out – top, bottom, and eye. You can also do this if you have metal heddles but you’ll need a pair of wire cutters to cut the metal. Be careful cutting the heddle eye to release the warp end, carefully bending the eye open so you can release the warp from the metal eye without snagging the thread and damaging it.
A matter of moments and a few cents worth of heddles and voila, you’re weaving again!
Currently reading A Murderous Procession by Ariana Franklin