Keep the test conditions consistent
Use the same computer, the same mode, and roughly the same time. Pause background transfers. Keep the test tab visible. Run one test over Wi-Fi, then connect a suitable Ethernet cable and repeat. Make sure the device is actually using the cable.
Read the differences carefully
If Ethernet performs more consistently, wireless conditions may be contributing. That is a useful clue, not proof of a broken router. If both perform similarly, investigate other devices, the service you are using, or the wider network path.
Try a small, reversible change
For Wi-Fi, move closer to the router and test again. Avoid changing many router settings at once. Ethernet ports, adapters, and cables have their own speed limits, so a slow wired result is not automatically a fault with your internet service.