Delete a file from a channel
Go to the channel where the file was uploaded and select the Files tab. Select the file, then select Delete from the More options 
menu, or at the top of the app.
Delete a file from a chat
Currently, the only way to delete a file you've shared to a chat is to delete it from the Files list.
Open Files on the left side of the app.
Under Cloud storage, select the cloud service where you originally saved the file, like OneDrive.
Go to the file you want and select More options
> Delete.
Recover a deleted channel file
If you deleted files from a channel and want them back, open the channel's Files tab and select Open in SharePoint. Once the SharePoint site opens, select Recycle bin on the left side of the page. This will show a list of all files deleted from every channel in the team. Right-click on your file and select Restore.