Since you explicitly said , that means you are on the pre-Anniversary Edition (Best of Both Worlds) or a deliberately downgraded setup.
Here is the definitive guide for getting RaceMenu working on Skyrim SE 1.5.97. You cannot use the latest RaceMenu from Nexus (v0.4.19). That is compiled for AE (1.6+). racemenu for skyrim se 1.5.97
This is a great question, because works differently depending on whether you are on Skyrim Special Edition (1.5.97) or the newer Anniversary Edition (1.6+) . Since you explicitly said , that means you