actually read the wiki

modules/settings/input.lua

@@ -50,6 +50,11 @@ if hl.plugin.hyprgrass ~= nil then
 			workspace_swipe_cancel_ratio = 0.15,
 		},
 	})
+	hl.gesture({
+		fingers = 3,
+		direction = "horizontal",
+		action = "workspace",
+	})
 end
 
 if Hostname == "mobile02" or Hostname == "mobile03" then