You can simply find your PayTabs account information on your Profile page, which from you can access information such as Profile ID, Merchant ID, Merchant Name, ..etc
From Dashboard > "Profile" tab, you can get the merchant ID (MID) as shown below.
The Profile ID
You can either get it from your Dashboard > Profile, or you can find it beside the profile name at the top of your page as shown below.
In case you have more than one profile, you may check the "How to differentiate and switch between profiles?" section in the mentioned article to know how to handle them and what you should do if you can't.