I invested some of my CPF OA into SingTel last year at $3.40. Should I sell now at a loss? Doesn't seem like the company will recover soon.?

I sold mine at a loss this week. However, I use cash, so I can deploy my capital into US growth companies to cover my losses.

Unfortunately as you use CPF-OA, I'd think you can only recycle your capital into other SG companies, which in my opinion I will not touch unless it's either our local banks, selected REITs or iFAST (need to check valuation...price is quite high now)

What was the initial reason you bought into SingTel? Do these beliefs still hold true now? Or are there significant changes?

If you believe SingTel will rebound at that's why you bought it previously, then you should buy more during a drop to profit more in the future. How you should proceed depends on your initial analysis.