Ok this collimating RC's comes up a lot and I'll just layout the routine to follow.
1: Collimate focuser to secondary mirror using laser (centre in secondary)
2: Collimate secondary to primary with Tak scope(read instructions)
3: Collimate primary to secondary with Tak scope(read instructions)
A few points: make sure you don't pinch mirrors by tightening too much and use a strong little torch on the Tak scope.
Also any tweaking to be done via star should be done on primary .
I've owned an RC10 and a RC12 and found both very easy to get good collimation with a good laser and the Tak collimating scope when done correctly.
Ken Crawford put out a little video showing the routine to collimate RC's maybe you could look for It or someone could share that with you.
ps. Apologies If this has been covered in this post already
Ok found the link to the video:
https://www.rcopticalsystems.com/support/index.html