My bad ... (these are importers) ...
A quick search on the Extension Warehouse reveals two (2) import extensions that say they can handle 3dm files:
Both are commercial extensions, but have trial periods.
There some oneline exporters, if you do a simple Google search…
but they are NOT free - just like any complex extension…
Thanks Dan. I also searched on the Extension Warehouse, I want to such an extension which can export 3dm not import one. 
Yes TIG. these software are same as Rhino, which can convert skp to 3dm.
Actually I want to make the process more smoothly. Its more better If all the things can be done in SketchUp. 
I know what you want to do from within SketchUp, but unless you write your own exporter, or pay someone thousands of dollars to do it for you, you are stuck with using something 3rd party - these tools are not that expensive; certainly cheaper that the other options.
Love the moron comment re ChatGPT (though one day when singularity is reached a its cousin may remember your disrespect and make up some story thar could bother your better half etc.
Seriously, and I dont believe this is going off topic too much, once I actually thought about what ChatGPY is and keeping that in mind learnt how to prompt and nudge it away from moron state I did/do start finding it very useful and a time saver.
excuse my typos - thick fingers etc. Can actually spell even without chatGPT
BTW I do fully agree with you. Good primary sources like this one should always be accepted as ‘primary sources’ rather than AI and do understand the frustration caused when others take the AI approach, but it is to be expected at first until people realise what DLMs are