Re-doing shifting cables is one of the more frustrating jobs, especially when it is an internal routing job (…they all are these days). Just go slow and expect it to take more time than you thought. The toughest part is getting the cable to exit the BB hole.
The two best tools for internal routing are
A flashlight to see the cable in the frame
A strong paperclip fashioned like a hook to fish out the cable from the BB hole.
The absolute best purchase I made was the park tool cable routing kit. It has a couple magnets and wires with magnet ends, and rubber gaskets that can grip onto Di2 cables, and a screw-end that can screw right into brake cable sheath. You can use the magnets to guide the guide-wire right where you need it and then attach your cable and pull it the rest of the way through.
The other trick (especially helpful for internal front fork brake cable routing where it has to go around the curve and exit in the middle of the fork) is a piece of dental floss crimped to your mechanical brake or shifting cable with the end cut off of the metal cable end cap, then use a vacuum cleaner to provide suction over the cable-exit point on the frame after feeding the floss into the entry point. It’s like magic and your floss will get pulled to the exit point, and you can pull the floss through, guiding the rest of the cable after it.
I bought that parktool kit to do internal cable routing on my circa 2009 Cervelo p2c.
Turns out that the tips of that park tool do NOT fit into the downtube hole of my Cervelo. And the magnet isn’t strong enough to grab the wire effectively from outside the frame.
I’m quite underwhelmed with the tool - it’s been a complete bust for me with my bike. It was actually easier to just trial and error the straight cables into the holes rather than try to push the Park tool tips into the frame to match up.
I think the best approach though is to prepare before you pull the internal cables and run some thin tubing over the wire before you pull it.
I don’t want to sound mean, but…you have internally molded cable stops in that bike…it pretty obviously won’t work when that’s the case.
I googled what an ‘internally molded cable stop’ is (haven’t heard of that!) - I’ve got those on the brake entry/exit hole along the toptub, but not along the downtube where the FD wire comes out before it enters the FD clamp. That’s the hole I’m referring to. No cable stop there, but the hole is like 3mm wide in the carbon frame itself.
Just turn the bike upside down or sideways in the stand, shine a light through the hole towards you and poke from the BB hole.
Yeah, did that - total pain in the rear! Had to trial and error it to finally get it. I’m not even sure I can run cable tubing around it the next time to avoid doing this again - that seat tube hole is so small that I’m not sure the tubing will fit through it!