Sweeping funds from a private key allows you to move funds stored on a paper wallet to a wallet in the Blockstream app.
Note: Instead of sweeping funds from a private key into an existing wallet, you can also import an outside wallet via its associated BIP39 passphrase. Importing is the correct option if you're more interested in simply adding your wallet to the Blockstream app rather than moving the funds into an existing wallet via an on-chain transaction.
1.
Select the Transact tab via the navigation bar at the bottom of the screen. Then, tap Receive.
2.
Tap the icon with the three dots in the top-right corner of the screen. This will bring up a small menu at the bottom of the screen where you can select Sweep From Paper Wallet.
3.
The app will ask you to enter the private key you wish to use to sweep funds into your Blockstream app wallet. Alternatively, you can scan a QR code of the private key with your camera. After entering the private key, tap Next.
4.
From this point forward, the process will look like you're making a standard Bitcoin transaction. Enter the amount you'd like to sweep from the private key and optionally increase the fee for the transaction by tapping Change Speed. Click Next once you have set these parameters.
5.
Confirm the transaction details, then Slide to Send to broadcast it to the Bitcoin network. You will then receive a message that the transaction was successfully sent.