Do you have the S10e, S10, or S10+? None of those have 5G capability.
If you have AT&T you may see a 5GE which is a marketing gimmick. It is really 4G LTE using things like three-way carrier aggregation, 4x4 MIMO, and 256 QAM. If you are having issues with that service, you should contact AT&T.
Actually, 5Ge is the same thing as 4G LTE. It's just a poor marketing gimick.