The messages or chats in Signal should be backed up if you don't want to lose them. Backing up also makes it easy for later restoration on a fresh install on new devices. To backup messages in Signal messenger, follow the steps below -
1. Tap on the three vertical dots to open the context menu of Signal.
2. Now tap on Settings.
3. From the Settings page, select Chats.
4. Then you will see a lot of options under "Chats" and one option under "Backups" called Chat backups. Select that option.
5. Now tap on the button named Turn on.
6. You will get a confirmation popup that your messages in Signal will be saved to external storage and encrypted with a passphrase.
Make sure to save this passphrase by writing it down in a safe place.
7. Now tap on the checkbox to agree that you have written down the passphrase since without it you will not be able to restore your messages later.
8. Now select Enable Backups.
9. On the chat backups page, select Create backup.
All messages from now on will be encrypted with your passphrase and will be stored on your device.
10. To know where your messages are stored, see the address below Backup folder.
11. From time to time, you can also verify your backup passphrase so that you don't forget it.
Tap on Verify backup passphrase to make sure you remember your passphrase and to check if it matches with the one you remember from your memory.