How do I open these trickle vents?

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This is my first post thank you everyone for having me!

I have old trickle vents that haven't been opened in years and despite trying many ways myself to open them I can't work out how to do it. I have tried spraying WD40 on these and waiting ten minutes and then putting a flathead screwdriver underneath the bottom and they still won't open! I don't want to brake them by trying too hard. Does anyone know how these are meant to open??

Thank you to anyone in advance!

 

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Update, I've managed to open them! Ah well!

Tried to delete the post but I can't

 

[crank39]

Try sliding sideways?

 

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They wouldn't slide at first as they hadn't been opened in years but after spraying with WD40 a few times and leaving and coming back to it they open now, thank the lord!