[tesseract-ocr] How to add desired character to existing language in tesseract 4.0

I found the a desired character file in source training data in chi_sim . So I guessed that in chi_sim.traineddata there is information of desired character. How can I add my unique character like ↑↓ into trained language? -- You

[tesseract-ocr] Invalid resolution 0 dpi. Using 70 instead.

I met a problem of Invalid resolution like bogon:OCR zhiyao$ tesseract /Users/zhiyao/Desktop/OCR/kindle3.jpeg ~/Desktop/OCR/kindle3 Tesseract Open Source OCR Engine v4.00.00alpha with Leptonica Warning. Invalid resolution 0 dpi. Using 70 instead. I changed different input images and file