Create a (bitcoin) new wallet and transfer all your funds from the key (or master key) you want to import in another wallet to this new wallet because those keys could be compromised
I would label the address COMPROMISED: DO NOT USE AGAIN in my wallet.
Learn how to run a sandbox in order to download and install ElectronCash in it to import your private keys into.
Even better if you keep the Fork wallet offline, copy the raw transaction, and broadcast it from another system. That way you make sure the private key never touches the internet from a Fork wallet (but just in case: don't use it again anyway).
My current setup (which I haven't needed since I created it, but that's not the point....) for dealing with untrusted Fork wallets is this:
I've added this to my toolbox for my Fork Claiming Service: a space laptop with 2 Linux distributions installed in dual boot. The first is to work on, the second doesn't have internet and now has 5 partition images:
1. A fresh installation with VPN
2. A fresh installation with VPN and BCH full client, synced up to 2010, and set to prune. And BCH's Electrum Fork.
3. A fresh installation with VPN and BTG full client, synced up to 2010, and set to prune. And BTG's Electrum Fork (using wine).
4. A fresh installation with VPN and BCD full client, synced up to 2010, and set to prune. And BCD's Electrum Fork.
5. A fresh installation with VPN and eCash full client, synced up to 2010, and set to prune. And eCash'es Electrum Fork.
The laptop doesn't have enough disk space to keep all full clients.
This setup makes it much easier to handle Forkcoins: I restore the partition I need, boot into it, import the address/pubkey, and let it sync. When done, I take it offline, enter the private key, and create a raw transaction to transfer funds. After that, I boot into the second Linux distribution to overwrite the first partition. This makes offline signing relatively easy without ever risking the private key to untrusted software.