This is really important. You’re responsible for the vehicle until it’s collected by the rental company, so you should make sure it’s left somewhere safe. You should also be available to hand the vehicle over because the rental company agent will do a full check for damage.
Once the agent is happy that the vehicle is in the same condition as it was when delivered, you’ll simply have to sign over the vehicle and that’s everything done. We would always recommend that you do the vehicle handover, rather than asking someone else to because no one knows the condition of the vehicle better than you so nothing will get missed.