From your wallet go to Levinswap
Swap between your USDC and xDai (As xDai and USDC are dollar-indexed stablecoins you should keep an exchange rate between the two.)
Once your USDC has been converted to xDai go to: https://www.xpollinate.io/
Choose the destination sidechain (BSC or Polygon) then choose the tokens to send (the xDai). The bridge will automatically convert your xDai to DAI for you.
You will then just have to pay the transaction fees (in xDai).
You have the option of choosing a reception address other than that of your wallet to receive your DAI.
Once the transaction is completed your tokens will be available on the receiving sidechain.