I got the base part of the helmet back when the old halo waypoint was out. But this new one is different. I just finished halo 3 ODST today and got my achievement for completing the campaign on legendary. But I don’t know how to get the other parts to the helmet on the new halo waypoint. Farther more, the new waypoint keeps telling me that there is some kind of error. I cannot stay on the waypoint for to long until it kicks me off and redirects me to the title screen of halo waypoint. Any information will do.
You just need one more game to go, seeing how from what you said. You’ve already beaten Halo 3 and ODST on Legendary, you just need to finish Legendary on Reach (you have to play solo, Co-op will not unlock the necessary achievement).
Once you get through that, head to waypoint and unlock the CQB upgrade. If it’s glitching out on you, i have no idea how to help or answer any relevant questions regarding that. Sorry 
Same here, I have all the achievements but don’t know where to go on the new waypoint.
This is helpful. Will I still get the helmet for doing the missions on co-op legendary? I know I won’t get the achievement, I don’t really care for achievments. I just want to unlock armour pieces. I yet to beat Halo 3, ODST, and Reach on Legendary.
> This is helpful. Will I still get the helmet for doing the missions on co-op legendary?
Yes you still get the Helmet if done in Co-Op Legendary 
And if you want the third attachment, you need to complete on legendary Halo 3, odst, reach.
I still play Halo Reach and I beat the campaign a long time ago on heroic but on the new halo waypoint it won’t let me get cqb