What should I do?

To the OP. I'm sorry that you did not get what you thought you were getting.

BUT based on the photos in the listing.
Unless you requested additional photos that you have not shared or messages that show the seller said it was a tech dash. I can see from the 3 dash photos in the sellers post that the dashes are the same where the teach should be. And they don't look like the tach shown in later posts.

The seller shared many posts about the condition of parts saying they were too rusted. And posted photos of a fender that had hidden rust after it was pulled off.

I think you made many mistakes here and the seller is not at fault.

If I had to guess based on the evidence presented here so far, the seller is 10% at fault and the buyer is 90%

That is based on not asking for many more photos before purchasing.

Just my opinion