Select the ‘Move’ tool, nothing else.
Then hover over one of both left vertices of the top part that is 964,7mm, drag it to the coresponding left vertex on the left part. Do the same for the other vertex.
You can also (in one go!) drag the little slanted top edge to the corresponding edge on the part on the left, also with just the ‘Move’ tool selected. (hover over the slanted edge to grab it)