How can I replace stone_slab with bottom only double_stone_slab in Bedrock edition?

I'll start by saying that a double slab, by definition is the combination of a top and bottom slab of the same kind. So trying to replace a stone_slab with double_stone_slab will NOT result in a bottom only slab. With that, what it appears that you're trying to do is replace any top stone_slab with bottom stone_slab, which is easy to achieve.

I began by filling a 5x1x5 area with top only stone_slab using the /fill command: _{1}

/fill ~ ~ ~ ~5 ~ ~5 stone_slab 8

From here, I then used the the /fill command adding the replace argument to specify that I wanted to replace all top stone_slab with bottom stone_slab: _{2}

/fill ~ ~ ~ ~5 ~ ~5 stone_slab 0 replace stone_slab 8

_{1. Specifying a block state of 8 designates a top only stone_slab.}

_{2. Specifying a block state of 0 designates a bottom only stone_slab.}

_{NOTE: I moved around while tinkering with command output between screenshots, so the coordinates are different, but the point is the same.}