A lot of de-soldering. Probably diodes are pressed. All of them individually collimated, thus most likely the replaced diode will have not ideal collimation.
A lot of fun is waiting for you.
The Chinese don't typically build things to be serviceable, not easily anyways. They have more of a throw away and replace attitude towards most products in my opinion. It doesn't mean that it can't be done but it would require a certainly level of skill, tools and luck.
I have the tools. possibly the skill but as this was an under used laser I decided to purchase but appears to have an issue. it engraves fine and cuts 8mm but no deeper. It would seem I dont have the luck.