You can extract your keys by using Ian Coleman's Recovery Tool. It runs locally in your browser and is fully open source. There is no sensitive information sent across the internet. If you want to be extra secure, you can save the HTML file and run it on an airgapped offline device.
- Enter your recovery phrase into the " BIP39 recovery phrase" box.
- If you have used an extra BIP39 Passphrase, you should enter it in the "BIP39 Passphrase" box. Otherwise leave it empty. That is not your app withdraw password.
- Select the coin your want to view/export from the 'Coin' dropdown list.
- Scroll down to the 'Derived Addresses' section. Find your address and copy the private key that corresponds to it. If you are on a mobile device, you will need to scroll all the way to the right to see the corresponding private key.
- The list of addresses is generated in the same order as the Coinomi app. You do not need to look through thousands of addresses (unless you have used thousands of addresses in the app as well). For example, the third address that was used in the app will be the third address on this list as well.
- If you sent coins out with that wallet, you may have "change" on "change" addresses. In the "Derivation path" section set the value of "External/Internal" from 0 to 1 to list the change addresses.
- If your wallet is upgraded with segwit, on the Derivation Path section of the page select "BIP84" and "BIP49" to display the "Default" and "Compatibility" addresses respectively.
- Coinomi allows you to make more than one wallet for each coin. If you are trying to find the address for a secondary wallet you created, tap+hold that wallet in Coinomi and select "... / Account details". Note its derivation path. The numeric values for "purpose", "coin" and "account" on the page must match the numeric values of the derivation path in the app.
- For Ethereum-based coins specifically, select the "BIP32" option on the "Derivation path" section and choose "Coinomi" as the client.
- For Smartcash specifically, for now use their official tool here: https://paperwallet.smartcash.cc/hdwallet.html
- For Groestlcoin specifically, for now use their official tool here: https://github.com/Groestlcoin-Archives/bip39
- For Decred specifically, they are in the process of being implemented on the main recovery tool
For more information about the Recovery Tool, refer to https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki