By default, the bot's prefix is it's mention (@Lightning) and cannot be removed. However, you can add custom prefixes that the bot will respond to.
Run @Lightning config prefix & click on the Add Prefix button to add a new custom prefix.
Mute Role (Optional)
If you do not set a mute role, Lightning will use timeouts for timed mutes. If the duration for a mute is over 28 days, you will be forced to set a mute role!
You can assign an existing Muted role for Lightning to use by using @Lightning config muterole <role>.
If you don't have a Muted role, you can create a new role in your server's settings, then use @Lightning config muterole <role>, then run @Lightning config muterole update to set the proper permissions in every channel.