Dear Анамарија Петин,
Good day!
Thank you for posting in Microsoft Community. We are happy to help you.
Based on your mentioned concern, to complete / delete migration batch, we have below official information article:
- Migrate other types of IMAP mailboxes to Microsoft 365 or Office 365 | Microsoft Learn
First: To check if migration batch completed, it can be checked from Classic Exchange admin center:

Second: To delete migration batch, it can be deleted from classic EAC and new EAC.

- Furthermore, you may also perform PowerShell command. Here is detailed information article: Manage migration batches in Exchange Online | Microsoft Learn

If I misunderstood anything wrong, kindly feel free to correct me and share with me some brief scenario for further analysis. I will further assist you accordingly.
I would really appreciate your kind cooperation.
Stay safe and healthy.
Sincerely,
Darpan | Microsoft Community Moderator