As far as I know Excel doesn't have functions named "2ndf" and "tab".
If you want a function to convert degrees to grads, just enter it.
If the degree value is in A1, then in B1 enter the function "=A1*0.9" to get the gradians value.
If you don't know how to enter functions in Excel, check the documentation or search online. It's a fundamental aspect of Excel and there's loads of information out there.