To obtain your player id, visit https://unchainedstats.com or https://gudecks.com/meta/user-stats and search your username.
Please note you will need to play at least ONE ranked match for your account to display on either unchained stats or gudecks. Once you have completed the game tutorial, participate in one ranked match to expose your player id.
Your ID will be in the url of your profile on either site. For unchained stats the format will be unchainedstats.com/player/{playerid}
For gudecks the format will be gudecks.com/meta/user-stats?userId={playerid}