To change the xDAIs on the blockchain from xDAI to Ethereum, converting them to DAI, the xDAI team provides a website that makes the transition easier.
The process consists of 2 transactions:
First: xDAIs have to b sent to the bridge
Second: From Ethereum side for the withdrawal of the DAIs to your wallet.
This transaction is necessary and has an execution cost of at least 0.0109 ETH, depending on the degree of network congestion.
To use the xDai chain bridge, you need a Metamask wallet or compatible with WalletConnect and xDAI. Here are the instructions for using the bridge, with video included
If you don't have Metamask, follow the instructions to install it and send your xDAIs to that address from the page corresponding to this functionality.