The maximum bandwidth available to a PCI-E 1x slot (the slot above your video card) is ~500MB/s. You would have gained a small reduction in overhead due to the 970 Evo+ being using the NVMe protocol, but performance figures would not be better than an equivalent SATA device. No converter can increase the number of lanes of this slot...the bottleneck is the motherboard/platform, not the converter or the drive.
The slot under the video card is a legacy PCI slot, which is much slower than the PCI-E 1x slot. That's why you can't find a converter for it; it would be more complex, more expensive, and much slower. If someone really needed to connect an NVMe M.2 drive to a standard PCI slot, they'd use a PCI to PCI-E 1x bridge card, then a PCI-E to M.2 adapter and they'd max out around ~100MB/s. There is no reason to do this other than to demonstrate it could be done, or to access the contents of an NVMe drive when absolutely no other options are available.
There is no practical (there are a few wholly impractical ways, but they would be worse and more expensive than just building a new system) way to get full performance out of an M.2 NVMe PCI-E 3.0 (or higher) 4x SDD on your system. The only interface that has the bandwidth to do this is the PCI-E slot the video card is in, and that is a PCI-E revision 2.0 slot, at best, so no passive adapter would enable full performance from a 3.0 drive.
Anyway, you are fussing over theoretical peak sequential bandwidth figures when they mean next to nothing for practical SSD performance. Refund your M.2 drive and adapter, buy the cheapest brand name 1TB SATA SSD you can find, and you'll likely never be limited by storage performance on your current system again.