Print substring of column based on position filter in awk

I have a file with following 3 columns

1   a1  abcd2   b1  acdb3   c1  abcd 

I need to extract/print rows based on substring of column3 on position filter (2=="b"), so the output should be

1   a1  abcd3   c1  abcd 

Based on (Print substring of column in awk based on filter) I have tried:

awk -F '\t' -v OFS='\t''{ $3=substr($3,2,1); print $0 }' a.txt