You’ve lowered the water level correct?
This part of the pool wall looks corroded (bubbling means rust underneath) & also like it doesn’t have a gasket.
You may try some silicone spray lubricant - let it sit a while & then carefully go at it with channel locks with a towel wrapped around the fittings to prevent marring them up & scratching the wall. If you see rust you should remediate it & paint the area.
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