This is super easy.
1) Take your delica, get *really* hot tap water and give it a good soak out, blast out all the crap and crud, especially between the blade and scales.
2) When it is hot, shake it out, blow out the excess water and let dry. The heat from the hot water should do this quickly.
3) Let it cool down, dry completely, then add a drop or so of your favourite lube to the pivot area. A little bit goes a long way...
4) Get some kind of an anvil, a small hammer (tack hammer or a mini carpenters hammer) and some kind of a flat nosed steel punch. An assistant helps too...
5) Get your helper to hold the knife on the anvil, with one side of the pivot rivet flat on the anvil. Take the punch and hammer and gently tap the top side of the rivet. Check lots of times, if you overtighten, there is no recovery. Check and try a couple of times, this should tighten things up nicely.
Good luck!
Clinton