Raspberry Pi 4 is a good choice. The wiring diagram and instructions are located here:
** Mini-Guide for Flashing SPI ROM Chips using Raspberry Pi 3B or 4 ** Please do not quote the entire mini-guide. Post a link instead. 19 Dec 2021: Warning! Thunderbolt 4 Docks will not connect to flashed Thunderbolt 3 controllers. Most CH341A Programmers output a potentially dangerous 5V...
www.tonymacx86.com
I can also provide (a) location of chip on motherboard, and (b) binary file to flash.
Meanwhile please have a look at above post to familiarize yourself with the overall procedure.
Update: Here's the location of BIOS chip on Z390 Designare:
View attachment 522023