As of version 3.0:

1. Go to the "Settings" menu
2. Rapidly tap the "Version" value at the bottom of the settings. 5 quick taps should open up the Dev Menu.
3. Click "Switch to Testnet"
4. Select "TESTNET"

Hello! You need to open the dev menu by:

• Go to Settings
• Scroll down to Tonkeeper's icon.
• Tap 6-7 times (fast enough!)
• Dev menu opens
• Switch to Dev mode
• Return to the Main screen.
• Press on The Wallet button.
• Choose "add a new wallet"
• A wild option to add a Testnet Account appears.
• Add a testnet account
• You are good to go!

Have a good day!

Hello how dose that work in the deskop version/ in the addon version?

Tonkeeper works by default on TON mainnet. If you decided to work on testnet, you will need to switch the app manually to dev mode. Open the "Settings" tab and tap 5 times quickly on the Tonkeeper Logo on the bottom. The "Dev Menu" should show up. Click on "Switch to Testnet" and make the switch. You can use this menu later to return to mainnet.