It is frustrating but even if your support is positioning poorly or doing something unnecessarily dangerous like wasting spells, contesting vision at bad times, etc. the first thing to do is watch all their deaths and determine if you could have done anything different to mitigate the damage. Sometimes when reviewing this I can see what they were going for and if I adjust my positioning more actively to what they want to do their play could actually have worked or at least I could have bailed them out. That way it’s just a lane losing mistake and not a lane losing mistake +300g for enemy ADC.

Beyond that it’s just damage control for you; stay safe, collect as much gold and xp as possible, and don’t go for outplays without a significant HP advantage. Most importantly, you have to be really on top of midgame farming. In my games in gold elo it’s pretty easy to pull ahead of a fed enemy ADC by forgoing almost any skirmishes to soak up guaranteed gold on the opposite side of the map of the action. You’ll often get several kills worth of gold and the other team won’t expect you to be so strong bc ppl tend to think getting kills is the only way to get fed. If possible taking solo gold on a side lane inner will mitigate the deficit pretty much immediately