Ensure you have BakkesMod installed.
Sign in above, then click the large purple Download Plugin button.
Open BakkesMod [F2] -> Plugins -> Plugin Manager -> Open pluginmanager -> Install from ZIP. Find the downloaded ZIP file, select it and click OK.
Press F2 in-game. Go to Plugins > Seekr, and paste your API Key, then click Save.
Stats upload automatically when you're in a Heatseeker match.