LERP is a very good script for changing Rot A which is the rotation of a block to Rot B, smoothly. After understanding LERP and using it in a few projects, you will always want something like LERP Position of some sort. For you, here is a script to help you understand.
A is the point where B (The position of the block) needs to reach. Speed is the speed that B needs to reach A. (Set B to the position where the block needs to stand initially, in a single frame) Just do this and you'll love it.