The user guide (including installation instructions) for ReaPack is here:
https://reapack.com/user-guide.
- Extensions menu > ReaPack > Browse packages
- Search for "Convert all takes pitch to rate"
- Right click on it and select Install v1.0
- Click on OK
It will download the script and add it to REAPER's Action List (Actions menu > Show action list) where you can run it.