I’m new and I need help to delete some instrumentals in order to complete my priece
Delete some instrumentals from what, exactly? If you shot your show using overdubbing, just select each instrument track and MUTE it using the MUTE buttons on the left of the track. Each instrument you do that to will vanish from your export and your live monitoring.
If you’re trying to do Vocal Isolation from a download MP3, that’s a lot harder. It’s very nearly impossible to come up with a good vocal from a show that somebody else mixed with instruments.