How does this connector come apart? (1971 Duster)

The terminal on the red wire was a problem for many Mopars over the years. Too many amps for the small round terminal , burned a lot of connectors in that location. Chrysler changed the design of the connector in 1975.
Here's a way to remove the round terminals from the plastic connector.
https://ksmetals.com/products/br014-3-16Once you insert the brass tube in the connector, it will compress the locking tabs allowing the terminal to be released. May take a few tries, but it almost always works.
These can be found in most hobby shops or online.