How do I attach my new flex cable to the old power button bracket?

I have bought a replacement power flex cable to replace the faulty one that was in my SE.

I need to attach the power button switch on the new flex cable to the power button bracket. I was expecting to just find a sticky blue part I could peel back, and then stick them both together, but this doesn't appear to be the case.

When I detached the power button bracket from the old, faulty flex cable, it was attached by some tiny spot welds or something. I really had to prise them apart with a scalpel.

Are they meant to be attached in the same way again? I have no tools to be able to do this.

Am I able to just wedge the power button switch between the bracket and the side of the phone casing? Will it move at all or would it be secure?

Appreciate any advice you can give.

The two separate parts:

How they should be connected - but there is no sticky to peel back to stick them together in this position: