I have 2012 and later mac mini with one bad the memory slot . can it be repair or replace ?

It will need a new logic board, which will cost more than it is worth. 

IMHO it would be best to just run it on one 8GB module or replace it with a new M1 Mac Mini.

Jah1son Said:

"I have a 2012 (later ) Mac Mini with a bad memory slot , can it be replace or replace ?"

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Replacing a Bad Memory Slot:

What makes you say it is "bad"?

Contact an AASP: 

Take this to an AASP (Apple Authorized Service provider), asking for assistance.

1. Go Here: Find Locations - Apple Authorized Reseller
2. Click: Service & Support
3. Enter: your location information
4. See: if there is an AASP nearby
5. Contact: an AASP that shows up, and find out more about the services that they offer to fix the Mac.

You’re welcome.