Trolls in champ select should be dodged anyone picking something they have a below 40% wr in if you see that in 2 roles consider dodging,
If you have 3 autofilled jungele mains or 3 autofilled midlaners Dodge. if you have an autofilled jungeler consider dodging if you have 2 people first timing a champion in ranked dodge if you see people lock in nunu and threathen to ruin ur game dodge, its pretty simple if you ever find them in champ select and you will every champ select have to check op.gg's to ensure ur not getting trolled.
Now lets say ur ingame, now it gets interesting and what to do depends on multiple situations which i will showcase
Scenario 1: your adc is 0/3 in lane and says gg go next and spams the surrender vote
At this point you should mute your adc and tell him its winnable
Now, there is various things he can do but that is generally the best way to get a losing adc to try to play well or atleast not afk or run it down.
Scenario 2: your toplaner gets in to a discussion with ur adc, ur adc is complaining that he is never there for teamfights but ur toplaner is playing a splitpusher ur toplaner gets angry and says ok ill troll and starts grieffing, Example of this farming ur jungeler's entire jungle, running it down mid, doing things on tilt , The thing to do here is tell ur toplaner that the adc doesnt know what he is typing about and to just try his best for you and mute the adc before typing all this,
Scenario 3: your jungeler threathens to afk the game because everyone is constantly flaming him
The best thing to do here is tell your jungeler to mute everyone and just play to his best ability
Scenario 4: your adc toplane and jungle want to surrender, they have completely given up on the game and simply wish to open mid
The best thing to do here is to tell them to all buy 1 pinkward and put it on the map and tell them to just try even if its a loss
Ofcourse every scenario is different, but here is 4 examples of things that you can do, despite me advising to dodge trolls if you see them in champ select i still felt the need to give 4 scenarios, and ofcourse there are not fool proof, someone will keep running it down despite you telling him to mute all and just do his best, they will not work for every single case but in some cases they do and will help and can make a game actually winnable.