Crease in lining paper and not pasted together to abother shet

Cut it out, the crease and fill, if there's a gap fill them to, and prepare

Sand the crease and the join line, apply a thin layer of filler to level it, let it dry, sand smooth, then repaint.

it may be impossible to remove completely without damage, in which case replacing the strip might be the only option for a perfect finish

If lining paper has creased and the joints haven’t met properly before being painted, unfortunately this cannot be fully corrected with paint alone. The correct professional fix depends on how bad the issue is: • If the crease or gap is minor, the affected area can be carefully cut back, filled with a fine surface filler, sanded smooth, sealed, and then repainted • If the paper has shrunk, lifted, or the joint is clearly visible, the best and long-lasting solution is to strip and re-line that section properly Painting over creases or open joints will always leave visible lines, as lining paper movement and shrinkage show through emulsion. Correct lining paper installation requires proper soaking time, correct paste strength, and tight butted joints. Once these steps are missed, cosmetic fixes are usually only temporary.