DMXE MARTIN GUITAR TRUSSROD. It appears to have nothing for the allen nut to screw into? There is a square threaded nut lying loose in front of the truss rod inside the channel

Contact Martin customer service.

heres their link
https://www.martinguitar.com/guitar-care/customer-service.html
Martin Guitar Customer Service Martin Co

To lower the action on an acoustic guitar:

Usually just the saddle needs reducing.

1. Remove strings (or you may be able to just loosen them). Remove saddle, sand down the bottom a little at a time. Restring and check action.

The action can be set as low as poss without any fret buzzing or note choking on all strings and on all frets.

2. Repeat 1

If the action remains too high then there are other techniques.

Later ...

To remove the knob, there should be a small hex key or allen screw on the side of the knob. Just loosen the screw. You don't have to remove it.

To tighten the nut properly, you may have to remove the back panel of the bass and hold the potentiometer from the other side. If allowed to turn too much, it could mess up the wiring.

You have several options:

1. Do nothing and live with the occasional problem.

2. Check your guitar cable and the battery connections for loose or intermittent connections/noise. Try to see if it's the amp responsible for the noise....ie, Is it caused by vibrations, or maybe static....especially in winter when it's dry. Your home power may have noise on the line, so borrow or rent a power conditioner which filters out noise. If that fails, go to 3.

3. Bite the bullet and pay a competent guitar tech/luthier to repair it. Most of these issues are due to loose/faulty connections. Should be less than an hour. Hey....It's a Martin.

3a. Pay a guitar tech to loosen the end pin connector so you can see if you can repair it yourself.

the only other solution would be an electrical short in the wires running from the tuning box to the input cable hole. take the tunner all the way out and make sure there are no loose wires. Make sure nothing is preventing the wires from making good contact.

Have the guitar setup at a reputable guitar repair shop. This is likely a truss rod setup problem which an inexperienced person should NOT attempt on an expensive guitar. It could also be that the slot in the nut is too low for that string. They can shim the nut if needed or replace it. There are several settings that have to be right to have good playability.

LIKELY the problem requires a truss rod adjustment. Best to take this in to a guitar shop for setup as one can do damage. The rod controls the "bend" of the neck of the guitar to set up string to fret clearance.

Hi. Your guitar may not be intonated properly. You might want to try to level and balance the height and strings all throughout the neck. The level at the rear half (close to the soundhole) can be slightly higher than the front half (near the headstock). This can be done be adjusting the truss rod, nut and/or saddle.
Note: You may want to get a guitar luthier to do the trussrod, nut and saddle adjustments as these are very delicate procedures.
:-)

Typically you have to unstring the guitar to get access to the insides.

Use a small miirror to view the insides. You may need to drag the jack out of the sound hole to resolder wires if they are broken. There should be three wires on the jack. One carries the audio, one the ground, and the third connects the battery when the instrument cable is plugged in.

After re-soldering the connections if needed, procure a piece of 1/4 inch wood dowel from your hardware store. Push the dowel through the hole where the jack goes and near the sound hole. Push the jack onto the dowel and then pull it back through the jack hole and pass the nut over the dowel and onto the jack threads and tighten. The extract the dowel rod from the jack.

It is near impossible to reach clear into the guitar body to put the jack back in without the dowel rod unless you have very tiny arms.

Most bridge saddles use allen head screws to adjust the height.