Frequency response of a FIR filter

Hello,

I'm trying to get a frequency response of a filter which I implemented with an object from the DSP toolbox, which is this one : a static/time-varying FIR filter.

https://fr.mathworks.com/help/dsp/ref/dsp.firfilter-system-object.html

Unfortunately, the property NumeratorSource, which specify the source of the coefficients of the FIR filter is turned to "Input port' because I have my own coefficients. Hence, I can't use the tools that can plot the frequency response like freqz or fvtool.

How can I do ? Does it exist a way to plot the frequency response of a time-varying FIR filter ?

Thank you very much.