If email is in the 'Junk' folder you have options: Select email in list and use 'Shift+J'

select the email and then you will see a 'Not junk' button in yellow message area just above the contents. Click on 'Not Junk' button

Right click on email and select 'Mark' > 'as Not junk'

Is this a pop or imap mail account?

What do you mean by " But file always reappears in Junk file." Do you mean the email you just set as not junk immediately goes back to the Junk folder ? Do you mean emails from that particular sender keep going to Junk ?

My apologies. The msgs in question are labeled Spam and are placed in Junk folder. When I attempt to move msg to inbox, it defaults back to Junk. Account is IMAP.

The server is auto setting the email as spam. Usually, the server uses a 'Spam' folder and Thunderbird pop accounts use 'Junk', unless you created the 'Junk' folder or it was moved over from one server to another server.

In the imap account 'Account Settings' > 'Junk Settings' You may have a setting to trust the server spam filter, which would mean Thunderbird could redirect emails set with a 'spam' setting to the 'Junk' folder.

When you say it is not 'Junk', this does not change the 'Spam' setting and the server seems to be moving those emails. Suggest you logon to webmail account and see if you can set up a filter to allow those emails.