Inside a DATA step program, you would need to use a DO loop. If you want the value of the FREQUENCY variable to change to 1, then you'd probably need to save the original value within your DATA step logic. Something like this untested code shown below.
. . . more code to read data either with INFILE/INPUT or SET statement . . .
. . . may also want KEEP or DROP statement here . . .
** grab original frequency value into new variable name;
orig_frequency = frequency;
** set frequency value to 1;
** Use original frequency value in do loop for output;
** control output in DO loop -- one observation will be output;
** for every iteration of the DO loop.;
do i = 1 to orig_frequency;
. . . more code to end program . . .