To restore the Message history tab in your Team follow these steps:
- Open the channel where you want to restore the Message history tab.
- Select the Files tab.
- Click Open in SharePoint.
- Go to Site Content in the SharePoint site.
- Select the Team Message History document library.
- Open the folder with the same name as the channel with the missing Message history tab.
- Open Messages.aspx.
- Copy the URL of the file in the address bar.
- Return to your channel in Teams and click on + to add a tab.
- Select Website as your tab type.
- Name the tab (can be Message history or something else).
- Paste the address you copied in step (8) in the URL field.
- Click Save.