usb2serial which programmer mac

I have searched but cannot find the answer, I have a USB2SERIAL device to reflash ATMEGA328 arduino Uno boot loader device and want to confirm which programmer should I select in the Arduino IDE?

I have a Mac, not sure if that will make a difference.

Many thanks

USB2Serial interfaces PC to the Serial port on the Atmega328.
You need a Programmer to reflash the bootloader, via the ICSP header pins. (Reset, SCK, MISO, MOSI specifally).

Nick Gammon's bootload installer sketch running on another Arduino can do that:
See one of these

If the part already has a bootloader installed, then you don't need to select a Programmer, that interface will not be used for the USB/Serial download to the Rx/Tx pins.