Login to Google Search Console
In the top left corner, you would see a dropdown list of existing properties (or domains) you own. If the domain you want to verify does not exist, then simply click on Add New Property option in the dropdown to add your domain which will open a popup like below
After entering your domain name, click continue to go the the next step
You can verify your domain via DNS records in your hosting or a URL prefix property. Choose whichever is more convinient to you and follow the process which is explained in detail in the search console.