Hi Sourabh,
This tab is for variable interest rate which means the physical interest rate is not determined yet.
And you can run TI10/ TJ05 to adjustment the interest rate to set the interest rate you want. Before doing this, the interest rate flow is locked and you can not do posting for it as the interest rate is not determined yet.
You may also refer to the link here for the document
Interest Rate Adjustment Data - Mixed Documentation - SAP Library
Regards, Feng