There are several venetian blind valence clips on Thingiverse, unfortunately they didn't fit or it was unclear what size blind they were for.
25mm is the width of my blinds - the clear plastic clip is the original/broken one, the white one is the printed replacement. The original clips had a little more tension, slightly popping the blind outward slightly. I am not even sure these were the original clips for the blinds, so I loosened the grasp slightly to merely a "firm" grip.
Designed in Blender. I used the original as a background image, combined with a couple of real world measurements from digital calipers. Hand-traced a 2D image before turning into an object.
The author marked this model as their own original creation. Imported from Thingiverse.