How to average vallues across multiple columns based on a date range?

Hi all,

I want to average values across multiple columns based on a giver date in the same row.
i have tried using
=AVERAGEIFS(C2:G7,B:B,">31/1/19",B:B,"<1/3/2019")
but it returns a #VALUE! error

I have included a sample book containing my values and formulae.

Will appreciate any help. Thank you!