One solution is to consider adding minerals, nutrients, and organics, for example humic acid, compost, kelp, epsom salt, molasses, potassium, phosphate.
Through the growing phase, sometimes lthe older lower leaves turn yellow. Analyze color of veins, and any other "offs", such as evidence of bad insects. Discard old yellow leaves near the bottom, away from the garden.
Peppers love what makes them thrive: sunshine, ventilation, water (not too much), organic ferlilizers, wasps (for bad insects), and bumblebees.
Hope this helps.