If you do not wish to move your balance to them, you will have to share the private key for the address that held those btc at the time of snapshot.
Coinomi has explained the procedure in detail and you wont have trouble claiming them.
Coinomi only seems to support sweeping on the Android app. There is no iOS app yet, and their beta desktop app doesn't have a sweep feature. And as far as I can tell all the web wallets are scams. So back to square one - no option outside of Android, unfortunately. I wish I could be proven wrong.