Receptacle Tester Showing Open Hot
Open hot just means that the wire that should be hot is not connected to the power supply. The neutral and ground are possibly still connected. This is a common way to switch receptacles by adding an extra (red) wire that goes through a switch.

You should check continuity between the outgoing (switched hot) wire at the switch and the red wire (going to the top receptacle) at the receptacle. If there isn't continuity then there is a break in the cable or it's not a switched outlet setup.

If that is the case and you want to be able to use the top outlets again you can connect the top and bottom hot sides of the receptacle and cap off the supposedly switched hot. You can then remove the switch and cap of the wires that go into it.

If there is continuity then you should be able to replace the switch and the receptacles will work again.