How do I get my logic board and PSU checked and are they repairable?

All I wanted to do was to apply new thermal paste and add a 2.5” ssd. That’s it. This 2015 27-inch iMac only has a 500gb Apple ssd

I opened the screen.

I carefully tried to remove the PSU. But the cables were near impossible to detach from motherboard. So I took both out the same time.

I applied the new thermal paste then added the HDD cable. Then reassembled per iFixit instructions.

Light 1 won’t light.

I have worked on 2007, 2010, 2011, 2012, iMacs, 2012 Mac book pros and mini Mac’s. I’ve built PCs for decades.

I applied all my standards. This is my first failure. This is tragically and purposeful poor engineering.

How do I get my logic board and PSU checked and are they repairable? Or do I suffer the loss of my investment that I was trying to protect and improve? (Which I have the right to do).