If you really want to boost your K then you can look at Potassium Sulphate.
What will help is if you feed the soil some Humic and Fulvic acid. I cant give you the exact science behind its impact but I have heard numerous growers talk about its benefits. I know it impacts the soil biology in a regulatory way, adjust soil ph and in general, is really good for your soil microbes. You can add Yucca into the mix as well, that stuff seems to be a golden nugget that I never knew of.
You need to accept that you have thrown out the biology of the soil. You are going to make things worse by throwing more stuff into the mix. If the first cause of the plants damage is overdoing it, then doing more of that is not going to help.
Take it from an organic grower, you cannot control things the way that you did with synthetics. The more research you do, the quicker you are going to realize this. Working with ecosystems do not allow you to cut corners. Meddling with these systems because you dont like the way the plant looks is a one way ticket to failure.
Trust me. Let them be, focus on ways to improve the soil biology, that is your only way to balance out the soil. Not adding more NPK into the soil. If you want to add anything for deficiencies, foliar spray.