There have been many complaints against Coinomi recently. The wallet is not fully functional and the project may have been abandoned.

I tried to recover a Coinomi testnet wallet in UniSat, but it required modifying the derivation path and it only generated the first address. It might be easier to restore it in Sparrow Wallet.

To recover your coins you can install Sparrow Wallet and go to Tools > Restart In Network > Testnet

Once you’ve relaunched in Testnet go to File > Import Wallet and then insert your backup phrase. Then click the “Discover Wallet” button to see if your coins are detected. I tested this and was able to generate the same addresses in both wallets.