Check to see if the trim ring below the nib coupler is loose. If the fit is not very tight you can sometimes pull the nib coupler out just a touch when tightening the cap. If so, consider removing the end cap and nib, then putting a drop or two of thin ca inside the tube to run down to the nib coupler, and press it back in to see if it fixes the problem. If that don't do it, I'm pretty sure you are going to have to take it apart to change the alignment, because the black Delrin insert with the threads is a very tight fit inside the cap tube. If you try to twist it without taking it out, you are almost certain to damage the threads. Of the two methods of alignment, I usually have better luck assembling the pen body, then aligning the cap to it, but it is possible to leave the cap assembled and adjust the threaded nib coupler. This is usually more difficult however because the depth to which the coupler is inserted directly effects how far the cap rotates. If you adjust the cap to fit the body, the depth to which the female threads seats is always consistent due to the lip on the center band assy seating on the bottom of the cap tube.
To disassemble the cap, I use a transfer punch with a dimple drilled in the working end. The dimple avoids unseating the finial insert when removing the finial assembly and clip. Then use a larger punch to drive out the threaded insert and center band assy. Be sure before reassembly to use a reamer or something to clean up any damage to the top of the threaded insert to avoid scratching your nib section. DAMHIKT To reassemble, seat finial and clip, then ensure that the threaded insert is seated fully down on the center band assy, then hand insert it into the cap tube just far enough that you can still turn it, thread down on to the nib coupler, turn the cap to align, then remove the cap carefully, and seat the centerband into the tube.
Let us know how it works out for you, (preferably with pictures