Training for IT Help Desk

Here a few resources that may help.

Microsoft 365 Adoption - check out the IT Professional resources
https://adoption.microsoft.com/en-us/

Microsoft 365 Help & Support - great for understanding end-user experience.
https://support.microsoft.com/en-us/microsoft-365

Teams Troubleshooting - Good starting point for common Level 1 type questions
https://support.microsoft.com/en-us/office/troubleshoot-6fa7c08a-6fd4-47a0-b275-90a5f60f1df9

Microsoft Learn/Documentation - Might need to hunt a bit for different products but there is a lot of good resources here for L2/3 support. Here's an example for Teams
https://learn.microsoft.com/en-us/microsoftteams/manage-teams-overview
https://learn.microsoft.com/en-us/microsoft-365/enterprise/?view=o365-worldwide

Microsoft Learn/Training - more structured approach which can lead to certifications. Good for L3 admins
https://learn.microsoft.com/en-us/training/