Is there anything I can stick onto a small roller blind to make it blackout?

[User63847484848]

Got a small window in my bedroom in a rental property with a white roller blind that lets a lot of light through. Is there anything adhesive I could stick onto the blind to make it darker? I don’t want to replace the whole thing as it’s a rental and not sure how long I’ll be there plus I’d probably mess it up!

You can get velcro/stick-on blackout material which you could stick over the whole interior window frame when you want the blackout effect.

I have a black out screen which I take with me on holiday.
Something like this