I know how to down-sample daily returns (large-sample data) to monthly returns (small-sample data) by using rolling windows, which feels like estimating a sub-sample from the population (something that makes sense based on what's given), but for some reason don't think it's as easy to go the reverse direction if starting from monthly returns and wanting to up-sample to daily returns, which sounds like estimating the population from a sub-sample (something that does not make sense based on what's given).
Is there a step-by-step procedure for up-sampling monthly returns (small-sample data) into daily returns (large-sample data)?