If you want to use this key pair in the future then make sure that you’ve already exported and saved it in the safest digital storage that you have. Otherwise, after deleting your key pair you’ll have no way to retrieve it back.

1. Go to Settings -> Messages -> Encryption.

2. Click on your Personal key that you would like to delete.

3. Click on Delete.

4. Read the warning message carefully and click on Yes if you want to proceed.