You can either buy a [PICkit3](https://www.ebay.com/itm/PICkit3-PIC-KIT3-Debugger-Programmer-Emulator-PIC-Controller-Development-board/400926122453) or similar programmer and an [SOIC 8 adapter](https://www.ebay.com/itm/1PCS-SOIC8-SOP8-to-DIP8-EZ-Programmer-Adapter-Socket-Converter-module-wide150mil/222122979750) from ebay to flash the PIC12F629...
...or you can build a simple PIC flasher for the COM port using the schematic provided here but you need to adapt the pinout from the PIC16F84 to the PIC12F629.