Filling gap left on wall after dado rail removal.

I am about to remove a wooden dado rail from living room wall and then plan to emulsion over existing paper. How do I conceal/smooth over the 2" gap in the paper where the dado rail was?
Any help would be appreciated!

polyfilla. get a nice wide trowel. Put it in the gap and run the trowel over it to get a fairly smooth finnish.

Sand it. Then re-apply pollyfilla in the areas that have been missed out. Sand again, you may have to do it a few times to get a really good finnish with no tiny gaps.

Use either orbital sander or a flat block of wood with sand paper wrapper around it. Make sure the block is wider than the gap. Place over the two good bits of the wall to make sure the middle becomes nice and level with the rest of the wall.