I couldn't find anything on the BL XR-31.
You should be able to get a manual for the Singer at
https://www.singer.com/support
I'm not sure, but maybe it is similar to the 5808C and some others. I had a 5808 that I gave my neice a couple of years ago. She doesn't really sew, but I thought she should have this one. I did some mending with it and some practice stitches as shown below. I don't know about the longevity of them, but should work for a while.
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Janey - Neat people never make the exciting discoveries I do.