blocked panel vent

I have a 1989 New Yorker in great condition.
A month or so ago, air stopped blowing out of the front panel vent whenever I have the air or A/C turned on. The floor and the window
vents are fine -- air and A/V blow out of these. It's just the front panel vent is "blocked". As the other vents work fine, this is rather weird.
What could be causing this? Is it an easy repair that I can undertake?
I really appreciate any and all help.
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