Watch your replays, learn what you did wrong, but most importantly realize -
Losing streaks are part of the climb.
As long as youre playing to IMPROVE, making mistakes and failing gives you the opportunity to learn what you should be doing. If you want to get better and get into gold, don't play to win.
Find out from your loss streaks what youre doing wrong - Maybe you misjudged your opponent's ability to tank the last 350hp or you forgot to check if they burned all 3 Corrupting pot stacks and ended up winning a fight you expected to be a favorable All-in.
Or maybe you sat on a charge of your
for 2+ minutes and never used it, so the jungler made a gank you could've seen coming.
Watch your games for that kind of stuff, and then play a few games with the sole focus of fixing those mistakes, not repeating them, and playing until they become second nature and just part of the flow. Then find new problems, isolate those and keep playing to minimize that mistake. You'll lose games in the process, but then you'll win games you would not have if you made those mistakes again. It may suck that you died to the Nautilus jungle because you forgot to deep river ward, but then a few games later they lock in a Rengar and you thank yourself for remembering to ward that brush or stay the hell away from any dark brush from now on....