Hi, @CLondon !
What in particular are you looking to add Meta Tags for? Is this for Search Engine Optimization, verifying domain ownership, or something else altogether?
If this is for SEO, there are four main places that you can add keywords to improve the results for your online store.The title tag and meta description are two of the most important elements of SEO. They are shown in search engine results, and provide information to people who are looking for things related to your products. You can see how that information can be updated here.
For Domain Verification we can't add the tag for you, however if you can elaborate on what you're setting up we can point you in the right direction and show you where the code goes.
Hope to hear from you soon so we can work through this together!