Launch the IFTTT app, go to the 'Search' page and search for "WIFIPLUG" or click here to open it in your browser.
Select the WIFIPLUG channel from the list then press the "Connect" button. You need to enter your login credentials for your WIFIPLUG account not your IFTTT account. These are the credentials you would normally use to login to the WIFIPLUG app.
Once you have successfully logged in, you will need to authorise IFTTT to access your WIFIPLUG account. You will need to accept this before you can use your WIFIPLUG devices with IFTTT.