In English it is called Bavarian (the other names are Bayern/Baiern/Boarn), but also a lot of my family is from up north, specifically North Frisian, which I can partly speak, which is now a minority language. There is no single German ethnicity though, there are multiple. German is a national identity, not a particular ethnic one. We all have our different cultures, dialects (some being unintelligible to other ethnic groups, which is why Standard German exists - a common tongue). For example most Germans will not understand Schwäbisch entirely, but the language and ethnic group is a German one, and even other people froma round the world would not recognise it as being part of German but some other language.
It's kind of like if you think about the United Kingdom or British Isles, British/Briton is not really an ethnic group, the Irish, the Scots, the English, the Welsh, etc are ethnic groups, they come from the British Isles like Bavarians or Swabians come from the German lands. In that same way the Irish have their language and culture, the Scots have their language and culture, etc, but the common tongue for mutual intelligibility is English which is the "standard" in the UK/isles - same happened in Germany with the formulation of Standard German to be taught in schools and used for official government (and encouraged, business). Even Swabians tell the time differently from others in Germany - something that took some time to learn as I found myself deep into Schwäbisch land lol - I still do not understand the Schwäbisch dialekt. Many of the ethnic groups are still home to where their original native tribes lived before Christianisation. Bavarians are direct descendents of Bajuwaren (emergence just before Christianisation and after Christianisation, they were what we call today the "Old Bavarians" - which if you go around Bavaria as a tourist you may come across places and things called "Altbayern" which this is related to, and then modern Bavarians descended from them and were the Bavarians in high middle ages. The Bajuwaren were comprised of many tribes like Sueben, Boier etc.
The same of course occurs in Spain, Italy, France, and quite a few European countries. You have probably heard of Catalonians, Asturians, Basques, Sicilians, Alsatians, Bretons, Occitans, etc - these are ethnic groups. Spanish, French, Italian, are national identities.
Foreigners, especially the Romans in particular popularised this by referring to all the tribes as Germans, but there is no single German ethnicity.