Use your drywall knife to scrape away the old joint compound from the seam where the tape is lifting. Slowly pull off the tape so the rest of the plaster comes with it.
Scrape off all the remaining plaster and texture paint from around the seam, anywhere there is loose material.
Press drywall tape over the seam from one end to the other.
Spread joint compound with a drywall knife over the whole strip of tape, from end to end. Get the compound flat and smooth.
Let the compound set for six to eight hours. Scrape the surface of it with your drywall knife to remove any peaks or ridges.
Apply a second layer of compound onto the seam, making the line of plaster a little wider. Keep it flat. Let it dry six to eight hours.
Scrape the second layer flat and add a third layer of compound, making it a little wider than the second. The plaster line should be 8 to 10 inches wide.
Allow the third coat set for at least 12 hours. Use a drywall sanding pad to sand it flat and smooth. Repaint the surface with textured paint.