When withdraw CPF how to report? which form?

I have a Central provident fund from singapore (foreign pension plan), and when I became a US person several years ago, say it was $1000usd. After several years, it is NOW $2000usd and I withdraw it in 2024.

Every year increment, I always paid tax (although  never take it out).

 

So, the questions is

1. when reporting in 3520 + 3520A, i put the amount of withdrawal is $2000usd. But, the actual taxable portion is only $1000usd. Where shall i indicate that the taxable portion is only $1000usd?

2. other than 3520, 3520A, FBAR, 8938, what form to indicate the withdrawal and define which portion is taxable.?

 

thanks