The IDV app lets you send information to UKVI without having to book a UKVCAS appointment. The IDV app verifies your identity and submits documents directly to UKVI.
Not everyone is eligible to use the IDV app.
Please wait for an email from UKVCAS inviting you to use the IDV app. You will not be able to log into the IDV app until you are invited to do so, and an error message may appear.