Sign into Google Tag Manager account from here- https://tagmanager.google.com and click on Create Account button.
Fill the required information, and choose Web (as platform) and click on create button.
Accept the Google Tag Manager Terms of Service Agreement, Tick the Accept checkbox at bottom and then click on Yes button on top
After accepting the Agreement, Tag Manager gives you installation code that you need to paste in your VINTCER website.
Open your VINTCER dashboard, from top bar click on setting and then choose Pro Settings
Paste the code inside Site header code and click on Save button