Indexicals is an argument ran by the affirmative that claims if the resolution is true under any framework, that is sufficient to prove the truth of the resolution under truth testing. Importantly, this means that even if the negative wins their framework, if the affirmative's offense still functions under their own framework, that would be sufficient to win the debate substantively.
Indexicals is clearly meant to be a trick, and most debaters intend for their opponents to either concede or fail to properly answer it. Answering indexicals is usually contextual to how the argument is presented, but you should argue that while the affirmative's burden is to prove the resolution true, the negative's burden is to prove the resolution false. Since a statement can neither be both true and false, it's illogical to justify affirming when the statement as simultaneously been proven false – that means the debate is unresolved and needs further evaluation.
Proving the resolution true under a specific index would be sufficient to affirm regardless of any index that negates since binary systems of obligations can generate opposite conclusions rendering all obligations and prohibitions impossible. The impact is that winning aff offense underneath one framework is sufficient to affirm. To say something is obligatory is just that it is obligatory under one locus of duty because the existence of an obligation doesn’t mean that there can’t be another obligation to do something else in different circumstances.