Need help completing challenges that require storyline missions to be active!

So I was wondering if anyone could help me out… I’ve been working on completing my challenges and noticed that there are a few that I haven’t done which require storyline missions to be active. I’ve missed the chance to do them as I’ve done all storyline missions on both playthrough 1 and 2 (I could do them in UVHM but I want to do them now and make them easier if I can) Is it possible I could join a lower level player’s new game and do the missions with them to complete them? Anyone fancy helping me out? Desperate. I really don’t want to lose the chance to complete them or risk failing them in UVHM.

Trying to think but from memory I can’t figure wich challenges/missions you’re talking about. If you could be more specific about which challenge maybe I (or someone else) could help.

'Save the Turrets’ is one challenge. There’s probably more but I need to look through and research them properly. I would really appreciate the help!

Save the turret. Yeah, I could had figured that one. Not essential and can be a real pain, Unfortunately I don’t have any characters to do it at the moment.
Dead air can be done at anytime once you completed This just in.

Damn it. Do you know anyone that could possibly help? Yeah, I just realised that, haha.