
Ours has no valves before end of low point drains. End caps are the 'valves', loosen or completely unscrew. Ours are crimp band sharkbites
(home depot) but if broken I'd replace with Flair-It fittings. Doesn't require a $60 tool for crimping band. Not sure I'd use sharkbite gasketed compression fitting on end of line?
Flair-It are a compression fitting but grip into both ID & OD of PEX tube. Valves or simple male or female adapter with cap or plug or. Appears that's what OP has. Either case Id cut clean above existing cap to replace. I don't see reason for following line inside.