You're stuck with 8GB on that generation.

The Dell XPS 13 9370 and 9380 both use soldered RAM. There is no replaceable module. If you wanted 16GB, you should have bought it that way from the start.

Dell moved to completely soldered RAM starting with the 9370 (2018) and continued through the 9380, 9300, 9310, and beyond. No upgrade path exists. Some very early XPS 13 models (like the 9343 or 9350) had one slot and one soldered stick, but those are years older and slower.

Your only real option is to sell the 9370 and buy a used or new XPS with 16GB. Or look at the XPS 15 (which often has socketed RAM in some configs) or a different brand like a ThinkPad or Framework laptop, where RAM is replaceable.

Future you is not going to find a hack to swap RAM on that laptop. Accept it and move on.