From what I could make out this has a threaded pivot. Take it apart.
Everything.
Lightly stone the pivots, apply a drop of oil then reassemble. When the pivot gets rather firm, twist the two halves three or four times then continue to tighten. It is hard to describe how tight to get the pivot screw. You just have to experiment.
When you take the scissors apart see if there is a thin tension washer. Sometimes these break. If it looks OK, don't loose it. If it's broke, you are going to have to replace it.
Again, you may or may not have a washer. Sometimes the threads are piened after setting the blade tension. A center punch or nail can set it if needed.
These are fun to figure out and fix.