I bought a treadmill last week and it has a 20 amp cord on it- my outlet is 15 amp. I'd prefer not to change the outlet, and have found a cord online that "steps down" the amperage from 20 to 15. My local electrical store said NOT to do that. Someone else suggested cutting the amp cord off and replacing the end with a standard 15 amp plug. Any better/other suggestions or feedback on the two I've listed? Thanks

If you have #12, install a 20 amp breaker and receptacle
DON'T Add any WEIRD CORDS like that.
Don't change the plug , or you increase risk of fire.

Wow. Listen to Strat.

You need to either ensure you have the proper wiring and circuit protection to run your treadmill, or return your treadmill for one that matches your circuit. THESE ARE YOUR ONLY TWO (correct) OPTIONS!