First make sure you have setup Metamask for usage with Polygon, if you need help with how, checkout this guide.
Head to 1inch at: https://app.1inch.io/.
Press the Ethereum button on the top right to switch networks.
Select Polygon from the list.
You will see a screen like below.
Press Connect wallet on the top right.
Accept the terms and condition by checking the box. Then press the metamask button.
Select the account you want to connect by pressing the check mark on it. Then press next.
Press connect.
Press the down arrow on the dropdown menu under you receive.
Search for USDC by typing USCD and press it.
In the top field, type in how many you want to sell.
Press the swap token button.
Press confirm swap.
Press confirm on the metamask popup.
You will see a popup to show that the transaction went through. You have successfully converted it at this point.
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