Can you put chocolate chips close to the blech on Shabbat in hopes of melting them?
It depends why you want to melt the chocolate chips.
Chocolate is a special food in that it is already cooked (see here) but turns into a semi-liquid once heated. The rule for dry solids that turn into liquids once heated (e.g., sugar, baby formula) is that they cannot be reheated above yad soledet bo (109-113 degrees F, 43-45 degrees C) because of the rule of yesh bishul achar bishul bedavar lach (see e.g., here)
As such one should avoid putting chocolate where it might go over that temperature. But as R Daniel Braude writes (Learn Shabbos, p. 139)
If [...] the liquid will not reach 109/43 degrees even if it will stay there throughout Shabbos, one may place it near a heat source. For instance, one may place a container of ice cream far enough from a blech or covered hot plate that it will soften slightly and be easier to serve, yet will never reach 109/43 [degrees].
Now there is a question whether melting constitutes a prohibition of molid (creating a new entity). Shemirat Shabbat K'Hilchata (vol. 1, p. 99) writes one is allowed to melt ice cream so long as one does not place it where it could reach 113/54 degrees. Similarly one can freeze ice cream as it is generally thought of as food.
With chocolate, it might depend whether you are trying to create liquid chocolate (which might transgress molid) or looking to soften up the chocolate chips to create soft chocolate (which would be permitted according to the sources above).