1) Download the DSD Talk Group file from RR and save it to the "Documents/p25rx" folder on WIndows or ~/p25rx/ on Linux.
2) Rename the file to have a '.dsd' file extension.
3) From the Talk Group Editor tab in BTConfig press the "Import CSV" button and select the .dsd file that you downloaded and renamed.
Your P25RX flash memory now contains a list of talk groups for your system!
The files are actually text, csv formatted files. You could append multiple files before the import if you have multiple systems. If you edit these files directly, you must leave the first line of the file intact with the "DSDPlus.groups" string.