No way to upgrade rtx 2080 chipset to rtx 3080 chipset …
RTX 2080 Mobile (TU104, the N18E-G3 variant): the chip uses the GB4B-256 package with 2228 solder balls, measuring 37.5 × 37.5 mm. This figure is confirmed by NVIDIA's official document (NPN-09178).
RTX 3080 Mobile (GA104): I couldn't find a confirmed number in the sources I searched. The commonly cited figure for GA104's package is around 1752 balls, but I'm not sure of it, so don't rely on it when buying a stencil or reballing parts.
What is certain is that the ball count and package size differ between the two chips, so a single stencil won't work for both. You also can't swap one chip for the other on the same board.