A family of Microsoft word processing software products for creating web, email, and print documents.
The simplest would be to do two Replace operations. The first would clear your manual changes. The second would change everything to your desired entry.
That is, Replace "-January" with "January" then replace "January" with "-January"
Otherwise, you could use the Replace button and Next button to manually skip ones you do not need to replace.
Third option, Replace (all) "January" with "-January"
Then Replace (all) "--January" with "-January"
If you have no intentional instances of -- in your document, you could simply do the replaces for the twelve months replacing all. This will give you some with two dashes.
Replace "--" with "-" after you have done all months.
Question, are all instances of the months that you have not manually changed preceded by a single specific character? If so, you could include that in your replaces.