If you want to use macro variable abc outside of macro, you need to make it a global macro variable:
%let x= 2020Q1;
%let y= 0;
%macro xyz();
%global abc;
%if &y =0 %then
%let abc = %sysfunc(intnx(qtr, %sysfunc(inputn(&x, yyq6.)),0,b),yyq6.);
%mend;
%xyz;
%put &=abc;
ABC=2020Q1
And you may want to know Scopes of Macro Variables
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