In edit mode, go to subtitle with or .

Select in cue with .

Framestep with and (if the in cue is connected to the previous outcue and you want to check/move both)

OR

Framestep  with and (if only the current incue is to be checked/moved).

Note that the cues follow the picture!

When you have found the right frame for your in cue, press to place it.