Grammar is important when writing English. One of the basic forms of grammar includes the correct use of has and have. Have is often used with I, they and we and other plurals such as squirrels. However, has is used with singular people such as she, he and it as well as terms referring to a single group such as team.
In this example, the team is a group of people. Although it contains many people, it is itself a single group. Hence, it uses has. This is why the correct term to use is ‘has been training’. It can take some time for beginners to master this concept. However, once you manage to do so, using have or has becomes second nature.