To set Signal as your default messaging app on Android, follow the steps below -
1. Tap on the three-dot vertical icon to open the menu of Signal.
2. Now select Settings.
3. Then select the first option, SMS and MMS.
4. Now tap on SMS Disabled.
If you're on Android 9 or below, you might get a dialog box for confirmation on whether you want to use Signal instead of the currently used messaging app.
5. Select Yes when asked if you want to use Signal instead of Messages or any other messaging app as your default SMS app.
6. If you're on Android 10 or above, you'll get a dialog box for confirmation similar to the below screenshot.
7. By default, Messages is selected but we'll have to select the Signal option if we want to set Signal as the default messaging app on our Android device.
8. Now tap on Set as default.
That's it. Now Signal will be the default messaging app on your Android device.