The private key of a BTC Eidoo wallet can be retrieved using the 12 words (seed) of the backup:
1. Connect to the site https://iancoleman.io/bip39/ (for more security the tool on this site can also be used in offline mode)
2. In the “Mnemonic” section enter the 12 words in box “BIP39 Mnemonic” and select BTC-Bitcoin inside the Coin
3. In the “Derivation Path” section select the “BIP49” tab and starting from the first line enter the following values:
Purpose -> 49
Coin -> 0
Account -> 0
External/Internal -> 0 or 1
4. Check that all data entered is correct and transferred to the section below “Derived Addresses”
5. If all the data is correct you will find the master key in the section "Account Extended Private Key", which will allow you to restore your BTC wallet on other platforms.