Gather any relevant evidence against the alleged smurf. This could include OP.GG links with descriptions of what seems suspicious, alternative accounts that you may have found linked to the user, any LFT discords that show they have a higher rank otherwise, or any other similar information. Make sure you have their account information such as their Gamercraft username, Summoner Name and Discord tag.
Compile this information and head to https://bit.ly/dontsmurf
Follow the steps on the page and enter: Your Discord tag, Gamercraft username, the Tournament Name, the smurf's Summoner Name, and their Discord tag.
Write out your explanation for why you believe this user is a smurf in the text field.
Add any screenshots or other evidence that helps build your case in the submission field.
Hit Submit and you're done -- You can expect a follow up e-mail within the next 24 hours with a status update for your report.