Hi @joanna26646
Here's a [https://www.youtube.com/watch?v=TkAVMjSmJiA|video] that ''in general'' shows what to do.
Note that not all remotes can be opened the same way. Some have a screw (under the batteries?) and others don't.
For the ones that don't you need to pry open the case along the seam using an appropriate [tools|Prying and Opening|pry tool] (examples only) or you could try using an old plastic credit card and see if that worked. Start near the LED light at the end or near a corner first.
Try not to break too many of the plastic clips that hold the case together, otherwise you'll need to use a small rubber band or similar to hold it together again once the repair is complete.