Sewing machine (Blackhall EH4)

The machine works great.The only problem is that the circular attachment where the needle comes down from keeps sliding too far down pushing the needle too far,so it cannot uplift the thread from underneath I managed to fix it a few times but it keeps sliding down.Ive circled the part which is the bother .
You can see there us a patch on the metal part where it should be sitting to do the sewing.It works great once the screw is replaced it should serve someone for a long time to come
I cannot use my right hand at the moment so am unable to undo the screw and replace it.
I would like this to go to a good home.
Thank you.

       
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