<p>There's PLA filament clogged in my Bowden tube, is there a best practice for cleaning it out or do I need to replace the whole tube?</p>
<p>Also, the couplings are totally stuck, so I guess those would need replacement too or are there ways to get stuck couplings off?</p>
<p>Click <a href="https://streamable.com/bi73e" rel="nofollow noreferrer">here</a> for a video.</p>

If you are able to force the filament from the interior of the bowden tube without causing damage to the tube, you will be able to determine the cause of the clog. My bowden tube clogged recently, but it was because I left the system idle with old filament inside. The filament broke from brittleness and the edge of the broken pieces managed to wedge against the tube.
I was able to use a "healthy" piece of filament along with great force (pliers pushing close to the tubing end) and remove the damaged filament.
Once removed, the new filament slid easily within.
Your PTC fittings may not have to be replaced if the tubing is not damaged inside and if the existing spacing meets your requirements. A PTC fitting has a ring of teeth which gouge and/or grasp the outside of the tubing preventing removal. It is frequently necessary to push the tubing into the fitting, then compressing the release ring followed by pulling the tubing.
The PTC fitting at the end where only the filament exits is probably a stock fitting. The fitting which has the bowden tube extending through it has been drilled and may be challenging to find. Your best source for such a fitting is the original manufacturer.
It's clear in the video that the threaded portion of the two fittings are different.