Take that dummy round and do this with your barrel:
The seating die does crimp, here are the instructions that came with your dies and an excerpt:
https://leeprecision.com/cgi-data/instruct/Pistol3.pdf
"Raise the ram to the top of its stroke and hold.Screw bullet seating die in until it touches the shell holder, then back it out three full turns. Lightly finger tighten the lock ring. Bullet depth is adjusted by screwing the adjusting screw in or out to suit. Bullets should be seated deep enough to work through the gun’s action. See maximum overall length on charge table. If crimp is desired, screw die in slightly and test until proper crimp is formed."
Here's a video giving you a general idea of how the combo seat/crimp die works:
As previously mentioned, you don't actually want to apply a crimp, just take out the flare. A pulled bullet should only show a very light (to no) crimp line.
Way too much: