On last years return I mistakenly reported >1k contributions to a traditional IRA. I do not have a IRA, but 401-K. Do I need to amend my return? Will it change my refund?

Contribution to a traditional IRA reduces taxable income by that amount and, thus, reduces the amount you owe in taxes. If your income is higher than the maximum income limit, then you can't deduct your IRA contributions.

However, you still must report these contributions on your return, and you use Form 8606 to do so even if the contribution didn't impact your return.

An individual who fails to file Form 8606 to report a non-deductible contribution will owe the IRS a $50 penalty. 

Roger, thanks for your response. I'm still a bit confused, I guess. I did submit a Form 8606 on my prior year return, claiming I'd contributed to a traditional IRA. However, I should not have. I do not have a traditional IRA, and simply misunderstood retirement accounts when I did so (i.e. that mine was a 401K, with contributions reported in my W-2). That said, do I need to amend last years returns to EXCLUDE the form 8606 and report NO contributions to an IRA in 2020, essentially. 

Yes, the best practice is for you to amend the 2020 return and remove the 1K contribution. In your amendment, the 8606 should go away however if it doesn't, then go to tax tools>tools>delete a form>delete form 8606. 

Since an 8606 was generated n your last year's return, you submitted this as a non-deductible contribution. If this is the case, it should have no impact on your taxes. Here is how to amend your 2020 taxes. 

1. Log into Turbo Tax 
2. When you reach the landing page, scroll to the bottom where your tax returns and documents are.
3. Select 2020, and click on the option to amend and change return.
4. Answer the questions about why you are amending
5. Once you begin working in your return, your refund monitor will reset to 0. 
6. Go to federal>deductions and credits
7. Retirement and investments>Traditional and IRA Contributions

@jgeorgenichol

BTW there is no legal requirement to ever file an amended return over a mistake. You might want to do so either to get a refund or to try make the the IRS computers/records correct, but there is no legal duty amend.