I soldered four male headers to the programming port. Here is what I did. I hope it helps.
The four headers I soldered were attached (not four individual headers). That helped because the pitch of the programming slots is larger than the standard 2.54 mm pitch. You have to work the headers in (stretch the outer two a little) but this creates a little tension on the pins after you insert them, which keeps them secure while you solder. You basically gain an extra pair of hands.
With the pins in place, you can solder three of the four (not the one under the cap). I used thin solder and came in with the solder from the side. Iron from other side.
Last pin. On the male header side (and on the side away from the other three pins) I cut the insulation of the pin to expose the metal of the pin. And that is what I solder to the board. Is it a little kluge? Yes. However, it worked for me. I’ve yet to put case back together. Not sure if this will cause a problem with reassembly. One issue at a time.
Regards, Mark