How do I convert input and output variables

[NJC1012]

In the off-design points, I wanted to control with N1 instead of thrust and T4, so I changed the balance module as follows:
balance.add_balance('FAR_core', eq_units='rpm', lower=1e-4, val=.017)
self.connect('balance.FAR_core', 'burner.Fl_I:FAR')
self.connect('LP_Nmech', 'balance.lhs:FAR_core')

The error is as follows:
RuntimeError:
Collected errors for problem 'problem79':
'case1' : Attempted to connect from 'LP_Nmech' to 'balance.lhs:FAR_core', but 'LP_Nmech' is an input. All connections must be from an output to an input.

How can I change it