Connect Keystone device
Step 1: Open SubWallet extension and click the account name to get to the account list
You would be directed to a list of accounts.
Step 2: In the account list, choose the "Attach account" icon.
Step 3: Choose "Attach Keystone account".
Step 4: Open your account on Keystone device, then click the "Scan the QR code" button on SubWallet and scan the QR code displayed on Keystone.
Afer importing the new account into the wallet, you might want to change the account name. Please follow this guide.
Please note that in order to see your assets after importing your account, your would need to manually enable the networks you want to use & have assets on. Please follow this instruction to enable the networks you want to use.
SubWallet automatically enable Polkadot & Kusama networks for Substrate accounts, but you can disable them if you so wish.