Roosevelt asked General Groves whether an atomic bomb could be used against Germany in December 1944. The answer was no, for a variety of reasons, chief of which is that they did not have enough fissile material (the bomb fuel) ready at that time, and would not have enough for a weapon until the summer of 1945. Given that it was expected that Germany would fold long before that (they did, in May 1945), it was not an issue. The first serious planning (choosing targets, etc.) for the use of the bomb against Japan began only in April-May 1945.

Many more details, including about the December 1944 meeting between FDR and Groves, are available here.

You might be interested in /u/restricteddata’s response (and linked post to his/her great website)here: https://www.reddit.com/r/AskHistorians/comments/aonhsl/did_the_us_threaten_to_drop_an_atomic_bomb_on/eg36b72

(Sorry for formatting, I’m on mobile)