Prime should only be used to treat new water rather than as a 'medication'.
A few questions just to get things clear in my mind -
Were you doing a fishless cycling, or intending to use the plants to do a plant cycle?
If it was a fishless cycle, how far had you got?
How many plants did you move, and what type of plants - slow growers like java fern or anubias, or fast growers like stem plants and floaters?
Plants use ammonia as fertiliser, and they don't turn it into nitrite or nitrate. They can use nitrate and nitrite in the water but they prefer ammonia as they have to convert nitrite & nitrate back into ammonia to use it and that takes energy. What I would do is a big water change to get rid of the nitrite, or several small ones if you don't want to upset the fry, and use Prime to dechlorinate the new water. Then treat it like a fish-in cycle and test every day, doing a water change if ammonia or nitrite rise above zero. With one baby fish, there should be very little ammonia being produced and the plants should be more than capable of removing it.
Shrimps do not create much ammonia either. I have a shrimp tank, a 23 litre cube. I have a piece of wood with anubias bonsai, another piece of wood with java fern and some Schismatoglottis preitoi (looks a bit like anubias which can be planted) These are all slow growing plants. But I also have red root floater on the surface and floating plants are particularly good at taking up ammonia.
About a month ago I changed the filter. Literally just took the old one out and put a new one in. I did not use any mature media from the old filter. The shrimps did not seem to notice, and they would have done if there had been a trace of ammonia or nitrite. The testers didn't register any either. I know there are bacteria in the substrate as there are in any mature tank, but the plants, especially the floating ones, would have removed a lot of ammonia, if not all of it.
I would treat your tank as now doing a plant cycle. Water change(s) to remove the nitrite in there now, and plants to do the rest. If you haven't already got some, I do recommend floating plants for shrimps and they are very good at ammonia removal.