How do I put a lower seat clamp on my Alinker walking aid? I have a walking aid called an Alinker http://www.thealinker.com/ 

It looks like a bicycle but it has no pedals and any bike shop can service it.

My issue is the seat it's a older style so has 2 bolts under the seat  mounted on the rails and I accidentally unscrewed all the bolts and the triangle shaped piece came out. I have the piece flipped upwards and its on the bottom of the rails. Can anyone here explain how to put this piece in the correct way. I am attaching a picture of my Alinker and the part in question.

I don't know much about bikes so please explain in easy terms.
OK, now I see what you're talking about.  I suspect the piece you have should go beneath the seat rails, with the cylindrical section pointing down and nesting in a matching half-cylinder depression in the base of the assembly.  The two ends of the piece have grooves (on the opposite side from the cylindrical face) that should accept the rails from the seat.  

Then the top piece is bolted down over the rails (with bolts from the bottom).  

The purpose of the cylindrical side of the piece you're wondering about is so that that piece can "rock" in the "cradle" created by the base, allowing forward/backward tilt of the seat to be adjusted.