Take a look at the
64-bit quad core CPU with SSE2 support
8 GB RAM
Full HD display
Mouse, trackpad or pen+tablet
Graphics card with 2 GB RAM, OpenGL 4.3
Less than 10 year ...
so this is my solution for those who may look for the same solution.
delete mesh, until it is back to the parallel part
extrude with edge snap on
select vertices that should align with bottom piece ...