ONT is no longer a NEO-based token, having launched its mainnet in 2018. Your ONT tokens are hence not accessible within the Nash Extension.

However, ONT wallet addresses and private keys are identical to NEO wallet addresses and private keys. You can hence use the private key from your Nash Extension wallet to access your ONT tokens on the ONT blockchain.

One way to do this is:

1. Navigate to https://o3.network/
2. Download the O3 wallet.
3. Create a new wallet by entering a wallet name and password.
4. Under the “Settings” tab, choose the option to import an existing wallet.
5. Enter either the private key or encrypted key for your Nash Extension wallet.

You should now have access to your ONT.

Please note that this is only possible for ONT because its addresses and private keys match those of NEO. Any other tokens sent to the Extension will result in a loss of funds.