Realme Flash Tool is used to flash RelameUI stock firmware files.
This is a direct link to download Realme Flash Tool for Windows.
The tool is provided by Realme on their forum. For integrity I have added the checksum of the file.
md5sum: 1315350998d26b5e2d3aa79e2897a9ea
Follow this guide to know how to install RealmeUI Stock Firmware.