Formula for MONDAY START on Any Year Calender Template

Hello..

Please kindly advise how to change formula to Monday Start? 

=DAY(IF(DAY(@JanSun1)=1,@JanSun1-6,@JanSun1+1))  -  Original Formula 

=DAY(IF(DAY(@JanMon1)=2,@JanMon1-6,@JanMon1+1)) -  Returned #NAME error

Any year expense calendar1.xlsx

KM