how do i hook up a netgear ax 1600 4 stream wifi mesh extender, it came with no instructions

The the extenders online documentation?

https://www.netgear.com/support/

AX1600 is a speed, not a model. 

What actual model do you have? 

There's a support site with access to manuals, firmware, install guides, etc.
Go to https://www.netgear.com/support/
Type in your actual model number and from there it'll take you to the above.
Its a great resource to start with.