if you want to transform waveform captured with oscilloscope to a usable lookup table, you're needs to downsample record from oscilloscope to a DAC clock used on your circuit. In order to do it, you're needs to apply low pass filter with cut-off below Fs/2 where Fs is your DAC sample clock, after that you can decimate filtered record to your DAC sample clock, you can do by skipping unused samples.
But you're needs to apply low pass filter before decimation, because if you do it with no filtering, you will get aliased distortions on the output.
If your circuit DAC has higher sample rate than your recording, then you're needs to upsample it. You can to it by adding zero samples and then apply low pass filter with cut-off at Fs/2 where Fs is your recording sample rate.