Managing contact access by blocking or unblocking users in Teams Free
Hi,
Are you using the mobile app? If you don't, please do so to access your account and block the user. If it's from Chat, click on arrow the arrow (>) **** beside the user's name, then, tap on their photo. Afterwards, the Block contact option should appear on the screen.
Another method is from the Community page. If you see a post from the user, just click on their photo and then Block contact.
When we block someone, we won't receive any Teams communications from them. They'll still be able to see our messages in group chats.
Block a contact in Microsoft Teams (free) - Microsoft Support