You could use a plain soldering iron to try to heat-press these in - Heat up the

iron and use it to press the insert in, wait for it to cool, then use like a hex nut

that's embedded inside the plastic. We strongly recommend our heat-set insert

tool for soldering irons because it's really hard to insert them straight otherwise

and you risk damaging your print!

Check out this video from Noe & Pedro that shows you how to do it

Comes as a 50 pack of M3-threaded inserts that are 4mm long.

 

https://www.adafruit.com/product/4255/6‐12‐19