Pick game modes? How to do weekly challenges?

Hi all I might be being really stupid and apologies in advance if I am.

Trying to complete some of the weekly missions that require certain game modes, problem is, I can’t find how to select those game modes.

I can do quick play, big team battle or ranked but there doesn’t seem to be an option to play a certain game mode. I know the modes I need might be part of the rotation for those but I’ve been playing for hours and am yet to get a single game on any of the game modes I need, if people have one week to complete these objectives it’s conceivable that with people that don’t have lots of time to play will miss out on even having a chance.

And welcome to a core problem right now. You cant chose your game mode besides quickplay and BTB. I think its just locked for the beta or for the first few days of the launch. We desperatly need to be able to chose our mode because I only like slayer and CTF when it comes to arena.

As for BTB I dont care what the mode is.

Glad it doesn’t just seem to be me then.

If it is just locked for the beta though how are any of us meant to complete the weekly challenges for this week if we can’t play the game modes that we need to for the objectives?