Hi @Phill16 and welcome to the forum. Removing the back of the remote to replace the batteries can be a problem the first couple of times as it it very stiff.
I find holding the remote at both ends with the buttons down and my thumbs on top and then applying pressure and pushing with one thumb and pulling with the other in the direction of the arrow is sufficient to remove the cover. Note the back only moves a few millimetres and can then be lifted off.
A number of people have found that wearing rubber kitchen gloves helps to give more purchase on the plastic components.
The following is a troubleshooting guide for remote controls which might be of interest.
https://www.sky.com/help/articles/remote-control-help-sky-glass
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