How to solve shift reduce conflict for if else statements in yacc?

I have a very simple context free grammar. There is a shift reduce grammar in if-else statements and I am confused how to solve this.

if_statement: if_match | if_unm
if_unm: if left_p boolean_values right_p stmt_list
if_match: if left_p boolean_values right_p stmt_list else stmt_list

How to transform this grammar to a nonconflict version?