Check along the carpet edge to make sure there are no screws holding it in place. The panel should flex slightly and pop out with some careful leverage with a slim instrument like a wall scraper or hacksaw blade.
Just try lifting it up, if it seems loose, then just tug the lower edge out and away from the bath. Once you have the lower edge out far enough, the top should clear the rim of the bath.
I am unable to check the screw at the back of the plastic of the overflow. I need to open the bathtub panel as suggested by previous members above.
From the image here, I could not use my finger to check as the hole opening is too small.
So confusion still reigns, how can that be the one and same thing as the screw you had in your fingers ? What I am trying to ascertain is have you broken anything and if it is it will require a new overflow...so a friendly plumber may be your best bet.
Btw, you didn't show pic or say if the "loose" screw had a thread inside it.
The loose screw is not a part of this at all. What has happened is - The OP has tried to undo Part B, the cover. The plastic part has stuck or seized to Part B, so has unscrewed with it, which has released the overflow part outside the bath.
The OP needs to first of all unscrew the plastic part (the nut) from Part B, remove the bath panel, reach behind and hold the overflow in place, insert Part A, then the plastic nut tightened up, then finally the cover Part B.
Please show some photos of the front and end of the bath, close up. Include where it touches the floor and the wall, and looking up at the rim of the bath.
You can copy and paste pics into your post. There is no need to link to other sites.
I rather think it is just wedged into place betweeen the floor and under the rim of the bath, and if so it will come away if you pull the bottom edge of the panel out towards you.
It might be blocked in by flooring or something. Can't see from your pic. Sometimes bathroom fitters like to glue panels into place with silicone sealant, but I can't see that.
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