Have you checked that both outlets are switched? Very often they are wired where only half is switched and the other is always powered. If that's the case, there's nothing you need to do except switch to the other outlet.
If both halves are switched and there is no constant hot in the box, then there isn't much you can do. If the power is turned off at the switched, a smart plug isn't going to be able to function either.
I suggest having an electrician check it for a constant hot and wire that up instead of the switched hot.
Have you checked that both outlets are switched? Very often they are wired where only half is switched and the other is always powered. If that's the case, there's nothing you need to do except switch to the other outlet.
If both halves are switched and there is no constant hot in the box, then there isn't much you can do. If the power is turned off at the switched, a smart plug isn't going to be able to function either.
I suggest having an electrician check it for a constant hot and wire that up instead of the switched hot.