AFAIK electrum unfortunately does only allow to create new 'receiving' addresses via the console,
but no change addresses.In order to derive more change addresses from your seed, you will have to use another wallet/tool to derive them.
Since electrum does not use BIP39, you will have to export the master private key of your wallet.
To do this, you will have to open the console ('View' -> 'Show Console' -> 'Console'-tab). Then enter this command:
This will print you out your mpk (will start with
xprv..).
Afterwards either import it into another wallet (using the derivation path:
m/44'/0'/1'/, for receiving-addresses:
m/44'/0'/0'/ ) or download this site (
https://iancoleman.io/bip39/) and run it on an offline PC to generate the private keys of your addresses (which you afterwards can import into another wallet).