The sketchup 2017 not supports 32-bit so my question is the sketchup 2017 can downgrade to 2016 version to support 32-bit
You mean the license of Sketchup 2017 can activate to sketchup 2016?
No. I didn’t write that at all. Each version requires its own license. They normally don’t sell licenses for previous versions but you should contact the SketchUp Customer Support people directly about any licensing.
what client can do if don’t they have 64-bit computer.
I already told you.
Or get a new computer.
Did you already buy a license for 2017 from SketchUp?